My Computer Crashes All The Time

I don't know what's wrong with my computer. It keep crashing all the time, I could be watching a video, writing a document or listening to a song and bam! it crashes without notice.
I'm running Microsoft Windows and have installed lots of PC Games from the Steam service, like Team Fortress, Left 4 Dead, Unreal Tournament.
My computer is 2 years old and this never happened before.
What's wrong?

I think your problem is due to a bad video card.
I suggest you turn off your computer, remove and reset your video card. Then restart and see what happens.
Also, try disabling some programs that may be causing conflicts.
If you installed something recently (before all the crashes started) try uninstalling the new software, that may be the cause.
If none of this works, I suggest you try regcure, from regcure.com.
It is a very useful application for a problem like this.