Go to your Control Panel and open your Device manager.
Open there the Display Adapter rightclick on the first and choose Properties.
Open the tab Driver and tell us which driverversion for that one is installed.
Do the same with the second one.
If you don't see there the Nvidia and the Intel give them permision in the BIOS of your hardware.

Hi, thank you both for your replies. I'm going through all your suggestions and will report back. In the meantime my drivers for my graphics card are up do date, 20th feb 19 and the driver version is... 25.21.14.1917 if that helps.

Hi, so after going through everything multiple times I've found out what's wrong and would really appreciate any advice to find a solution. Bearing in mind that everything worked perfectly in Movie Studio 13 for years until the preview window vanished, it's MS15 plat that is the problem. Anyway, after checking everything I find that MS15 does not like it if I have a 4K 30fps video clip with a png logo overlay. Basically, I have a png image logo that displays throughout the entire video for branding. When I remove the logo image from the 4K segment of the video everything works fine. No issues with rendering crashing, freezing or quality. Why this logo over 4K causes an issue I have no idea and the problem is, I need the logo to display throughout. Most of the video is 1080p 60fps, the 4K clip is 30fps. the logo is a png. At first I thought it was because I was trying to render a video containing 2 different files at different frame rates but when i removed the logo just from the 4K part, all worked fine. The logo over the 1080p 60fps segment was fine. Any reason why MS15 would have a problem with a 4K clip with a png overlay and not MS13? Thanks again for any advice.

@GP99 If you provide a little bit more information about your source media, I would try to replicate your issue using my source. I have 1080-60p and 4K-30p and can generate a PNG logo. What resolution is the PNG logo? Is your 4K-30p source media video actually 4K (4096x2160) or UHD (3840x2160) resolution?

Apparently you can finish your project using MS13, or is there a reason you need to produce it using MS15? If you need to use MS15, then there may be a work around.

@Eagle Six Hi and thanks for replying.

The PNG logo dimensions: 2122 x 1902 pixels - 32 bit depth - 173KB. The size of the logo is obviously reduced on screen so it appears just in the right corner.

The resolution of the source media video properties show as 3840x2160. This footage was taken on an iphone with the settings supposedly at 4K 30fps.

I have now completely uninstalled MS13 as no matter what I tried the preview window appears to have vanished for good and due to editing the old MS13 project now in MS15 it is only possible to edit in MS15 which is fine as long as I can get MS15 to work correctly.

I have managed to find a work around which seems effective but would be really interested in your thoughts. I made a separate mp4 1080p 60fps render of the 4K 30fps clip and then removed the original 4K clip from the project and replaced it with the new render with the logo overlay still in place. This worked so I was happy. However, about 5 minutes after this, MS15 completely stopped working, I mean I couldn't edit or do anything. I'd open the software and it would just crash or freeze. Nothing would fix it so I completely uninstalled and reinstalled and only then would it fully work again allowing me to render. At 79% of the render it crashed. At the exact point where it crashed I cut / removed about 5 seconds of footage. It then worked and finally rendered and completed my video in full quality.

I have no idea why this software is so temperamental but it's causing me to waste so many hours trying to fix things and I know this won't be the end of it. I'm so ready to buy some new premium editing software that is actually reliable. The only plus is that MS15 renders in a fraction of the time that MS13 did. Anyway thanks for your time.

@GP99 just read your previous post, I want to take a shot at replicating your project and will return shortly with a reply.

@GP99 just re-read your previous post and I have a question. You state the UHD (4K) footage is from yout iPhone, which to my knowledge usually record in variable frame rate. How did you convert that footage to 1920x1080? What program did you use?

Can you download the free app Mediainfo from here: https://mediaarea.net/en/MediaInfo

Start Mediainfo and select the 'View' tab, then scroll down and select 'Text' mode. Then select the 'File' tab and load your original source media from your iPhone. Then copy and paste the results or screenshot of the results. It will display a long list of metadata codec information for moth the video and audio in that file.

I think your original problem may have been caused by the variable frame rate (Vegas and most NLE's like Constant Frame Rate), and then perhaps the conversion yu did to 1920x1080 has caused an issue with the render with a corruption at the point render fails.

@Eagle Six

Hi, sorry for the delay. I have done as you requested and the info is as follows.

General
Complete name                            : E:\iphone Footage\IMG_3765.MOV
Format                                   : MPEG-4
Format profile                           : QuickTime
Codec ID                                 : qt   0000.00 (qt  )
File size                                : 1.11 GiB
Duration                                 : 3 min 29 s
Overall bit rate mode                    : Variable
Overall bit rate                         : 45.4 Mb/s
Encoded date                             : UTC 2017-08-09 13:10:30
Tagged date                              : UTC 2017-08-09 13:14:00
Writing library                          : Apple QuickTime
com.apple.quicktime.make                 : Apple
com.apple.quicktime.model                : iPhone 6s Plus
com.apple.quicktime.software             : 10.3.3
com.apple.quicktime.creationdate         : 2017-08-09T14:10:30+0100

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L5.1
Format settings                          : CABAC / 1 Ref Frames
Format settings, CABAC                   : Yes
Format settings, RefFrames               : 1 frame
Format settings, GOP                     : M=1, N=30
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 3 min 29 s
Bit rate                                 : 45.3 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Rotation                                 : 180°
Frame rate mode                          : Variable
Frame rate                               : 29.970 (29970/1000) FPS
Minimum frame rate                       : 28.571 FPS
Maximum frame rate                       : 30.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.182
Stream size                              : 1.10 GiB (100%)
Title                                    : Core Media Video
Encoded date                             : UTC 2017-08-09 13:10:30
Tagged date                              : UTC 2017-08-09 13:14:00
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
Codec configuration box                  : avcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 3 min 29 s
Source duration                          : 3 min 29 s
Bit rate mode                            : Variable
Bit rate                                 : 80.0 kb/s
Channel(s)                               : 1 channel
Channel layout                           : C
Sampling rate                            : 44.1 kHz
Frame rate                               : 43.066 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 1.99 MiB (0%)
Source stream size                       : 1.99 MiB (0%)
Title                                    : Core Media Audio
Encoded date                             : UTC 2017-08-09 13:10:30
Tagged date                              : UTC 2017-08-09 13:14:00

Other #1
Type                                     : meta
Duration                                 : 3 min 29 s
Bit rate mode                            : CBR

Other #2
Type                                     : meta
Duration                                 : 3 min 29 s
Bit rate mode                            : CBR

I've managed to get everything working but only if I re-render the 4K file as mentioned in my previous post. The info here is of the original 4K iphone file that wouldn't allow anything to work. Thanks for your thoughts and help, much appreciated.

@GP99 Thank You for posting the Medainfo on your iPhone source media. As you can see it is variable frame rate, not good. So your workaround to convert the footage to 1080 probably also included converting it to constant frame rate. If you convert/transcode your original UHD iPhone source to a more Vegas friendly UHD in constant frame rate, you may find that it is not the UHD footage causing the issue, rather the variable frame rate.

What program are you using to convert the iPhone footage?