It depends on which thermal compound you used as to whether or not it is electrically conductive.

If it is, your CPU is unlikely to be fried and after cleaning it up it should work (famous last words).

If none of the fans spin up, then you've prolly got hard electrical problems. You could start by disconnecting the motherboard from the PSU and the disk drives. Then plug in a fan and switch on. Build on that step by step. If the fan doesn't work, then the PSU is phut. A voltmeter might help.

I think it may actually be the board that's the problem in the end as I've now tried a different CPU with no luck. Still need to test the CPU that's been cleaned to make sure it's ok though. The PSU's fine though as I'm using it just now.

Thanks for your reply :-)

Normally in such instances, first thing you have to do is check the devices individually with another working machine.

Normally most of the thermal past wont shortened any device. Reason is mainly in contains semi-conductors and avoid the current flow, not completely but up to a certain level. That small current wont damage devices.