Freezing computer

[TomJ]

hi, my computer is freezing completely - its not lag or anything it just stops everything stops even the mouse n then when the freeze stops it starts off where it stopped from like if i was listening to music it would completely stop, it used to be frequent. It does it some days and some not but on the day it does it it is very bad - i end up rebooting and then it even sometimes does the freeze on the windows logo start up. Even when it doesn't freeze the start up is always slow now. Plus I'm having frequent problems with my direct 3d, on this day i was playing COD4 and all of a sudden it went all black and started to lag then when i got visual, it was all white but some things i could see, i tried another game, same whiteness! Before i was on COD4 i got a direct 3d error msg saying...

Direct3D error 0x0x8876086a (D3DERR_NOTAVAILABLE)
15 addresses:
(unknown)(0): cnc3game.dat+36323 (unknown)
(unknown)(0): cnc3game.dat+4410979 (unknown)
(unknown)(0): cnc3game.dat+3704705 (unknown)
(unknown)(0): cnc3game.dat+3522910 (unknown)
(unknown)(0): cnc3game.dat+3602266 (unknown)
(unknown)(0): cnc3game.dat+4393392 (unknown)
(unknown)(0): cnc3game.dat+3419754 (unknown)
(unknown)(0): cnc3game.dat+3640369 (unknown)
(unknown)(0): cnc3game.dat+3644004 (unknown)
(unknown)(0): cnc3game.dat+579642 (unknown)
(unknown)(0): cnc3game.dat+1454777 (unknown)
(unknown)(0): cnc3game.dat+1348923 (unknown)
(unknown)(0): cnc3game.dat+9606 (unknown)
(unknown)(0): cnc3game.dat+41286 (unknown)
(unknown)(0): cnc3game.dat+36323 (unknown)
(unknown)(0): cnc3game.dat+4410979 (unknown)
(unknown)(0): cnc3game.dat+3704705 (unknown)
(unknown)(0): cnc3game.dat+3522910 (unknown)
(unknown)(0): cnc3game.dat+3602266 (unknown)
(unknown)(0): cnc3game.dat+4393392 (unknown)
(unknown)(0): cnc3game.dat+3419754 (unknown)
(unknown)(0): cnc3game.dat+3640369 (unknown)
(unknown)(0): cnc3game.dat+364004 (unknown)
(unknown)(0): cnc3game.dat+579642 (unknown)
(unknown)(0): cnc3game.dat+145777 (unknown)
(unknown)(0): cnc3game.dat+1348923 (unknown)
(unknown)(0): cnc3game.dat+9606 (unknown)
(unknown)(0): kernel32.dll+94311 RegisterWaitForInputIdle+73
Because of the severity of this error the game will now exit.

I have scanned and no viruses, cleaned registry with 3 programs twice today and i do that every 2 days or so.

my comps stuff is
AMD Sepron Processor
2800+
1.60 GHz, 512 MB of RAM
Physical Address extension
Nvidia Geforce 6200 (i have checked for latest update for the driver and it is the latest).

Any ideas and suggestions to my problem?