Hi everybody!
Few days ago I purchased new additional harddisk 250GB so that to format it in NTFS for rendering and storing larger video files than 4GB. My system harddisk is still in FAT32 (both two partitions). So, I started to render out a 2-hours wedding movie, the target file to be a dvd mpeg-2. After one night I saw that the system is frozen when the rendering process was on 66%. Mouse, keyboard, task manager, etc. - everything was absolutely like if you watch it on a photo picture, i.e. totally inactive! Then I was shocked when I tried to restart the computer from the restart button. The result was a big nothing - no any loading of the system, even the monitor didn't run, although that all the computer, monitor, mouse, keyboard were light active (i.e. with diodes ON). The next time same-same happened on 40%, then the third time - on just 3% (!?!?!?!?!?!)
So, does anybody know what the reason can be?

I'd try to get ALL drives to NTFS. You might also check where the "temp" folders currently are and change them to point to the new drive as well.

Rendering to MPEG2 is also very CPU intensive. Heat could be an issue since you've added another hard drive. Lowering the "rendering threads" in the Vegas preferences may help (i.e. run a test dropping it from 4 to 1).