I have just experienced an identical problem to the above on my 4 year old Dell desktop. It occurred out of the blue when booting up 2 days ago, having been trouble free until now. have tried all the checks I can think of (which is not many).
Interestingly, I have a 128mb ATI Radeon 9800 Pro graphics card which I think is the same as the one in the above post.
Can anyone help with this?
I would also be interested to know if Ken(above) found a solution. Was the graphics card at fault?