I recently upgraded to Vegas 13, from Vegas 11. It is possible to import MP4 files (containing AVC video only, no audio) into time line but instead of video preview I get a green screen. In Vegas 11 the files could be previewed without a problem. Quicktime is installed, 7.7.4, not the latest version but one that was recommended to work with Vegas 11. Anything to try?
Mediainfo information is:

General
Complete name: E:\Glee\Season 5\GleeS05E01.mp4
Format: MPEG-4
Format profile: Base Media
Codec ID: isom
File size: 1.63 GiB
Duration: 43mn 58s
Overall bit rate: 5 306 Kbps
Writing application: Lavf55.22.103

Video
ID: 1
Format: AVC
Format/Info: Advanced Video Codec
Format profile: High@L4.0
Format settings, CABAC: Yes
Format settings, ReFrames: 4 frames
Codec ID: avc1
Codec ID/Info: Advanced Video Coding
Duration: 43mn 58s
Bit rate: 5 302 Kbps
Width: 1 912 pixels
Height: 1 072 pixels
Display aspect ratio: 16:9
Frame rate mode: Variable
Frame rate: 23.976 fps
Minimum frame rate: 12.048 fps
Maximum frame rate: 16 000.000 fps
Color space: YUV
Chroma subsampling: 4:2:0
Bit depth: 8 bits
Scan type: Progressive
Bits/(Pixel*Frame): 0.108
Stream size: 1.63 GiB (100%)
Color primaries: BT.709
Transfer characteristics: BT.709
Matrix coefficients: BT.709