If the monitor is plugged in then it works fine (I get the self diagnostics window), although when it is plugged into PC it fails to leave standby mode. Is this just a dead graphics card? PC boots up but obviously I can't see anything to diagnose the problem.

Thanks in advance

Dear MattNWR

I assume you have checked the proper operation of the PC with another graphics card first ?
If that card functions , obviously the other graphics card has a problem with either the software setting, or with the hardware itself.
To make sure : try it in another computer and see what happens !