I love how everyone pops in here acting like they are professionals on PC components. Some of the responses I've read so far have made me laugh.
Check your video card drivers, mate. If you are running Crysis2, Farcry 3 , and Planetside for hours at a time and not experiencing any video issues like 'hieroglyphs', discoloring, or freezing, the chances are your video card drivers are not agreeing with the game software somewhere.
If your video drivers are up to date, check your motherboard bios. There may be a chance your particular video card has some sort of compatibility issue with the motherboard. Usually, if there is a real noticeable problem, they will have a firmware update for your bios.
These will be the first thing to try before assuming what everyone else is assuming your issue is.
If your drivers/bios are up to date, the second thing I would look at is your memory. You can download memtest86 for free, put it to a CD or flash card, and have it run all night while your not using your system. That will let you know if you have bad sectors in your memory, and depending on your brand, they will usually replace them within 1-2 years.
It's doubtful your CPU or power supply are to blame, so I wouldn't worry about that. Reason being, Crysis and Farcry eat more power than Diablo 3 would for graphics.
And just because people will !@#$% about what do I know, not only am I A+ certified, MS in Computer Science, I have worked at companies such as Monarch Computers, Tiger Direct, and most currently Cisco for system repair. I have 6 years of college dedicated to my craft, and 10 years of hands on work experience.