Quick spec:
CPU: i7-7700k at 5GHz (HT off)
GPU: EVGA 1080ti SC2 Hybrid
RAM: 16GB Corsair Dominatir Platinum at 3000MHz
With all the extras, M.2 drive, SSD's etc etc etc
I have a 30min Nvidia Shadowplay file (3440x1440) that I made some simple edits to and rendered OK a few days ago, it took 3hrs to render using a custom profile but I decided the quality wasn't quite good enough so I changed a few settings, now it won't render, it starts OK then stops at a random point and just freezes.
So to troubleshoot I reinstalled Vegas 13, turned GPU acceleration off and went back to practically a standard render template (MP4 Internet 1080p, with just a resolution change to 3440x1440) and trimmed my video down to 20seconds just for testing purposes, it rendered fine...
So one by one I started adding my custom settings one at a time and rendering it to see which option was causing the issue, I finally narrowed it down to number of slices, my 20sec clip would render with 11 slices but not 12. So I started a fresh session, put the whole video clip in and used the last working render settings (11 slices), but again it failed even though it worked with the shorter clip?!
So maybe it's not as black and white as just one of the render settings causing my problem. My CPU temp is about 78°C while rendering so that should be OK.