I have ATI RADEON 64Mb DDR.

I didn't have any problems installing it at all.

I would do as Beta Spanky said, just check that you have inserted the card correctly, double check your Mobo BIOs settings.

Re-install back to VGA graphic drivers then try installing the proper drivers again.

If you try all this and still nothing, you may have a faulty graphics card bud.

But once again double check by trying the card in a other rig before you chuck-it.