Radeon X850-XTPE 3D tests failing-cannot run any games!

I do not use my bedroom pc much for games so I have no idea when this problem first started. I am using an Asus A7N8XE Mobo and Athlon XP3200 with 1Gb Ram and 700Gb HD's with 600Gb spare. The power supply is an 500w Antec which runs 1 dvd rom and 2 dvd dvdr's plus 3 HD and floopy.
I installed UT3 and it would not work (which is common at the moment I understand for lower spec systems till the patch is released). So I uninstalled UT3 and thought I'd play Americas Army but it would not load and said I should remove the armyops file. I then went to DX Diag and tested the 3D to find it failed on 7, 8 and 9. I have tried updating to the latest ATI drivers and even trying the older ones back to 11/06 but still 3D is not working.
Before I try removing the card and replacing it with my GForce 4 4600 spare emergency back-up I was hoping someone may have had the same problem? As I said I have not played a game on this pc for months and of course there has been many windows updates which may be a problem now?
I am concerned the X850 maybe duff because I purchased it second hand although it was supposedly unused.
Oh and another thing I had noticed since buying this card was that sometimes when starting the pc and it getting to my sign in page the whole page was covered in a white grid! Because this went away after restarting every time and it only happened now and then and seemed to disappear completely after updating the ATI driver I never gave it a second thought.
Let me know if you need any error codes etc.
Thanks

Bad RAM??? Where did you come up with that?

Sounds like the card's 3D end is toast and on it's way out.

If He installed the card THEN the problem, and only then the problem occured. Remove the card obviously.