Installing a GeFORCE FX 5500 OC

It could have to do with the overclocking, I suppose. (Unless "OC" means something else here...)
The integrated graphics card should be disabled in the BIOS if it can be.
Also, check to see that any additional molex (power) connectors are plugged into the end of the card if it has them. (I'm not sure if the 5500 did...)

Jam it back in, in the dark.

Originally Posted by rendr

The molex connector shouldn't be a problem if there is one because the 3D core would not be powered, but would work enough to show stuff and get into Windows.

A good number of graphics cards I've seen (especially nVidia cards) with additional power connectors won't even allow the system to boot if the power is not connected, so I think his situation still might be that, assuming the card has the appropriate molex connector.

There's nowhere I can't reach.