No video after installing new graphics card with VGA-DVI adapter

"I ended up disassembling the computer ENTIRELY to dust it off and buy me some time to consider the approach I'd take.

Then while I was reassembling I tried turning it on without any video card to see if the motherboard would beep (if it didn't, then something would be very wrong with it). It did beep, and I installed the card afterwards and it worked perfectly.

So, I had no chance to try resetting the CMOS, but quack's reasoning seems very right and should be tried by anyone experiencing a similar issue."

"Does the motherboard have an onboard graphics chip?

If it does, that's the first thing to try. Remove the 9800GT completely (having a card in might disable the onboard graphics), plug the monitor into the motherboard's VGA output and see if you get a picture.

If you don't then it would point to the motherboard being dead.

If you do, then you can verify that the machine still works.

Make sure you've got the 9800GT drivers. Put the card back in and double check it's seated properly. If it still doesn't work can you check the card in another machine? If that doesn't work then the cards faulty. As it's new you should be able to take/send it back for a replacement. Actually if you bought it locally it might be worth taking it back anyway and asking them to double check it's OK.

Update

You need to double check that the old 8600GT drivers will work with the 9800GT. If they're not compatible that might explain the lack of graphics. In that case you need to install a 8600GT then uninstall the display drivers & use the Windows VGA drivers. Then install the 9800GT which should work at VGA resolution. You can then install the 9800GT drivers.

If they are compatible then the problem lies elsewhere."