Windows 7 Crashing / PC Shutting Down

Okay, a little background... a couple months ago I had issues where the computer was randomly crashing. When I say crashing, I mean it was like someone pulled the plug. Just completely lost power. It would be fine again for a couple days, then do it again. I did the SFC/ SCANNOW and it never found anything wrong. Boot repair never found anything either. Malwarebytes was always clean. Finally, the last time it crashed, I could not get it to boot to the desktop. I started getting BSOD c000021a. HP told me I should do a complete system recovery. I backed up my data and did the system recovery. After several attempts, it finally worked.

Not knowing what was wrong, I tried to be as systematic as possible. I completed all windows updates, as well as driver updates. I slowly added software to make sure there were no issues with the installs (Office, Adobe Reader, Corel, Firefox, etc.). It has been running perfectly for about a month.

Today, I installed iTunes. The only other thing that changed was Firefox updated itself from 27 to 28. Since the iTunes install, it has crashed twice. Each time I was able to reboot and it was fine. In the Event Log, the only ERRORS I could find were the ones saying the system shut down unexpectedly. Not sure how else to mine data out of there.

I did a system restore to put it back the way it was before the iTunes install, and so far so good. Could iTunes really be causing this problem? If so, why, and is there anything I can do about it? I have several iPhones and iPads as well as a lot of music and movies that I need iTunes for.

Thanks for your help!

Well, it did it again and shut down. I noticed that it did it while I was watching a YouTube video. This morning when it did it I was watching the Olympics online. Not sure if it is a coincidence or not, but I thought it my be video-card related. I have a Radeon HD 4650. I went to AMD and downloaded the newest driver package. Watched a couple of videos without a crash, although I don't know if that's a good test or not.

Crashed again, and again it was right when I closed a video. Does that automatically mean the video card is bad?

Ran the Video Card Stress Test that comes with HP (HP Support Assistant). Made it through test 1 of 3, but during test 2 of 3 the computer shut off again.

No sounds at all. No lights, just goes dark.

I cleaned it last month when I was getting the BSODs. Thought it may have been overheating.