White screen loading portal

[mxxx]

Hey,
Please help, I really want to play portal but when I load it it just displays a white screen. I know its running as I can hear sound and I can move the mouse. I have even managed to start a new game but just get a completely blank white screen with the mouse pointer on it and dont know how to get it working properly.
I'm running a radeon 9800 AIW
Athlon XP 2400
1gb DDR 400
Windows XP SP2

Episode 2 runs fine but portal just wont work, i've tried running it in a window and forcing DX8 mode but still it displays with just a blank white screen

 

[Jas0n_X]

Try reinstalling Portal or getting new PC.

 

[Acepilotf14]

Uh, Jason, that's from two years ago.

 

[Mong0!]

whoa!

 

[Acepilotf14]

Uh, Mongo, that's from seven months ago.