My computer is screwing me!

Hello,guys,it's andreicucuiet still trying to make some kind of sense of PC gaming.

Anyway,my first problem appeared in DOW2.After playing for some days (30-40 fps) the next day I started the game and it lagged(20-30 fps).With no apparent reason.Now Just Cause 2 is doing the same thing.The game ran silk smooth for 3 days and now it lags.FRAPS says it goes at 30 fps,but what I am seeing is more like 20 fps.The lag can definatly be seen.Also my grahpics card just stops somethings and displays for me pretty patterns and colours.Great.Also,now,after 5 mins of Just Cause 2 the screen goes black,but I can still hear the game.

Ati Gigabyte 5770HD,2 gigs of ram,AMD Athlon 5600+ X64,Windows 7 x64.Help.

• Video card is going bad
• Video card is overheating when playing a high 3d application. Those "pretty colors & patterns" sounds like alot of artififacting.
• Bad drivers or currupted drivers

Yeah,I belive the graphics card is dying.It is new,and has a 36 month warranty.So I can get a new one for free.Oh well.