Desktop won't power up

[Magnum]

I replaced a video card fan in a Compaq desk system.

Now it will not boot.

Power is getting to the power supply.

And I changed out the switch on the front cover, but still nothing.

What else can I check ?

[Magnum]

Thermal paste had extended beyond the GPU chip.

Once the excess was cleaned off, computer started powering up and graphics card is running O.K.