Computer not booting up

[dabotsonline]

My computer's CPU heatsink broke recently but that has now been replaced and the fan is spinning as normal. However, when I turn the computer on, although the fan spins the BIOS does not beep. Also, the monitor turns on for a couple of seconds (but doesn't display any information), then returns to standby. I have checked all the connections into the computer and motherboard (including the connection from graphics card to monitor), tried changing the graphics card and monitor, but without any luck.

Any ideas?

Thanks, Nick

 

[Lan]

what specs?