bizarre graphics problem - black screen

Hi everyone,
Im hoping someone can help me fix this so i can get back to playing GW.

I upgraded my mobo/cpu to an amd 64, and asus a8v-x.
My graphics card is a geforce 6800le, and its running on xp sp2.

I can run dxdiag, and all the tests are fine, everything works.
When i try and run gw on 16bit colour , i get the sound and the mouse pointer but no graphics - black screen. The mouse pointer changes when it moves over a link to the support page (i tried clicking is how i know what it is) so the program must be running, but no picture at all.
If i try on 32bit colour, the screen sticks on the 'loading 100%' window and the whole screen flicks on and off - i have to hit the windows key to get the mouse back to rightclick close the app.

Graphics on the xp desktop are fine. Ive tried the lastest nvidia drivers, and 5 other legacy nvidia drivers - same thing.

Is my graphics card bust? I really dont want to have to buy a new one after getting this one only a year ago

Increase your virtual memory. They tell you how on the GW support page.

ill try that when i get home, but ill be surprised if its that - ive got it on default xp amount atm, with over 1gb free space on that partition, and 1 gb ram. That should be enough, shouldnt it?

Im gonna assume you have DX 9c, so Ill say try it on another PC, if you can, see if you get the same thing. Doing any overclocking? You didnt mention, so I thought Id ask. Also, why 16 bit color? Most Windows apps now run best in 32 bit, so Im curious.

yup, dx9c.
Im not overclocking anything - i tend to try and keep stuff on default settings because i know i dont know much about hardware.

I dont have another pc or graphics card to try it with unfortunately - i bought this one because my last one broke.
The 16bit colour thing was during my initial 'keep turning settings down/off to see if you hit a point where it works' phase. I thought id mention it to see if anyone recognised the flashing/black screen symptoms.

hasnt helped at all
It was on default, i changed it to maximum (3072), hasnt made a difference.

Ive just tried installing an older game which used to work and runs on directx 9.0b (sacred plus) - it shows me the startup adverts, the loading bar, and then bizarrely the water animation that the menu should sit on with no actual menu.

Does anyone have any idea how i can fix this, short of trying to reinstall everything?