SoT completely shuts off my pc

Your computer shutting off can be several things.
Power Supply failure, RAM voltage reset to a lower setting, Harddrive overheating, CPU overheating. It may just be coincidence that it started happening on that specific date.

There are other things that can cause your computer so shut off, but these are the normal things I come across in my day-to-day.

Also, when was the last time you updated your graphics card drivers? If it was long ago, you should update them.

My first approach to these kinds of issues is to open up your tower and use canned air to blow out the dust and debris that PCs collect.
Ensure heat sinks for CPU and Video Cards are nice and debris free; as well as the fans for the case and power supply.

The next step is to physically remove RAM, Video Cards, Audio Cards, Hard Drives, etc. (all peripherals that you feel comfortable taking out).

Blow the PC out again being careful not to cause any damage.
Put the PC back together and boot normally.

Give the game another try and see if the problem persists.
If it does, check with the vendor of the PC and its devices for up to date drivers...like @Danish-Crusader mentioned.

Driver issues tend to put up errors on either side of a shutdown; whilst unexpected, immediate shutdowns like you describe are more temperature related.

Hope this helps....good luck!

@lil-fokker Right, I should have noted that he should clean the computer... I was in a hurry, I had stuff to do(Lousy work related stuff) =P

Anyway, the driver thing can shut down the computer like he mentions, the one I worked on at work today was having that specific issue with the drivers not being up to date, causing it to turn off at random.

Anyway, OP, let us know if cleaning it and updating drivers worked so we can clean soundly =P

@danish-crusader
Roger that!
Drivers can be such a nightmare.

I've seen the very same shutdowns the second you'd connect any device to a USB port. Drove us nuts.
Especially because every device that we had of that series was affected for months before an update was published....and that was nearly a thousand devices in a large school district.
Students and teachers losing tons of instruction time whenever they would connect mice and/or usb headsets to netbooks.

UGH!!!

@lil-fokker Sounds like a nightmare, glad it wasn't me =P
Though, seeing as I work at a school too, it might be me in the future... Not looking forward to that =P