Graphics Failure

Got a bit of an odd one
The graphics output on my media centre has stopped working. The computer starts fine and boots into windows (i can hear media centre start up) but there is no output to the screen. The screen behaves as if it is getting a signal, no standby mode or 'no signal' messages.
I have tried the graphics card in another machine and it works just fine.
I have swapped the RAM and tried another card in the computer but no difference.
I am tending to think that the motherboard has given up, one memory channel died last week, irratating but not life ending. However no graphics on a media center is a bit more critical.

Motherboard is an ASUS A8N SLI SE with a 3500+, 2*2Gb DDR ECC RAM and a 8600GT
Any ideas before I buy a new board and bits

t'would be a knee-jerk reaction to blame the mobo, but lets try the alternatives;

Could you have possibly set a resolution not compatible with your display, or set a refresh rate too high?

no settings have been changed in weeks and I get no graphics output from boot.

I'm blaming the mobo as I have swapped everything else but the CPU (I have no spare) and because of the other recent failure of one memory channel

I just find it odd that the computer still boots and windows starts and at no point do I get any beeps or any graphics output :S