I am trying to remember how mine worked. I think the heatsink was held down by a clamp
and the fan screwed onto the heatsink.

Sounds like either, screwing it down stress the motherboard causing a connection to break (or be made) or maybe the screw is causing a short circuit.

It shoud make no difference really as it is just mechanical.

I am having the same problem with my desktop. excatly same i have changed almost everything except motherboard so can somebody tell us which motherboard we should get please

What wattage is your powersupply? example i have a 750w xfx powersupply. what type of cpu do you have? have you ever gotten the video to work properly?

I think its 750 2 but i am not sure its intel core2 duo E series. Processor is fine i am pretty much thinking its a mobo. I am trying to find the same mobo but i cant find it online.

The mobo serial number is MCP73M02H1 its of FOXCONN. Can anybody help me to find replacement motherboard