If your computer doesn't pass the POST process then it doesn't have anything to do with a driver, your computer hasn't gotten to the point of even trying to load drivers.
It's not about the graphics card being so heavy that the motherboard bends, it's that video card may be touching a metal...
If you have a speaker for beep codes, a good POST(Power On Self-test) will usually generate 1 beep. I have a feeling your computer is not POSTing.
You could buy a power supply tester to test the power supply. I understand it is new, but faulty components aren't unheard of.
You could have a...
Have you not applied thermal paste since you realized you didn't put any on? I would try correcting this first and see how your computer runs... Clean the old paste off first and then apply the new thermal paste.
Have you tried reseating the GPU? Maybe reconnecting the cables from the PSU to the GPU? Your cat jumped on the tower, maybe it rocked something loose inside?
Bios don't rollback on their own, generally speaking. I guess if the update was corrupted and the motherboard had backup bios, it might reference that, not sure.
I'd try running memtest86 -- usually BSODs are caused by faulty memory.
Try unplugging your older Hard Drive that is at 100% usage all the time. Are you sure your computer isn't overheating? Might check the performance monitor and see what speed your CPU is running at on average.