Actually this thread can be deleted as after updating to Build 10061 the problem had gone away and Sony Vegas stopped crashing.

On my PC (running build 10049), when I try to open Sony Vegas Pro 12 it closes when it gets to "Creating Windows". It was working fine a few days ago and I haven't installed any updates. It also...

The new build 10049 fixed my l crashing problems! I suggest if you have this problem then update.

How did you revert to 9926?

Correct.

I'm unable to tell you my motherboard or CPU because now every time I boot my computer it freezes but I do have an ATI Radeon HD 7750 graphics card and 8GB of ram.

Whenever I try to run any game on my PC after 1 minute, everything freezes and I have to reboot. I've tried rolling back my graphics drivers but that didn't work either.