got an 8800gts640 using a P5vd2-x motherboard . Using XP and the computer is 3 years old .

Was playing a game when it froze and purple lines appeared on the screen , rebooted the PC , it had purple lines on the screen while booting up but not in windows . In windows its is running slow when looking at websites ( seems to redraw the screen while scrolling down) .

There's a yellow exclamation mark next to the video card on the device manager . Says " cannot start device error code 10" . Did a search on that but nothing really helpul .

So my mate lent me his spare 8600 card , i put that straight in but the computer had the same purple lines got into windows then crashed , reset itself but wouldnt get by the very start off boot up , saying an error message that sounded serious and wouldnt even boot up at all .

Put my original card back in and it booted up with the purple lines that then dissapeared once in windows , it said windows had recovered from a critical system failure . So i can use the computer in windows but if the website has any graphics on it it scrolls down very slowly . Also i cant load up any games as they will crash quickly .

Should my friends card have worked just by plugging it in as its an nvidia card as well? Not sure now if my video card is broken or the motherboard . I havent re-installed the crivers which i will but im sure that wont make any diffrence .

don't be so sure about the drivers not making a difference, do that first and holler back. It does sound like a hardware problem however. more like memory however. run memtest after you reinstall the video drivers.
http://www.memtest.org/