Hi eli4247 and welcome to Tech Support Forum
There are quite a few potential causes for this one. Check the following:
*Check the obvious first—Did you reattach the display to power and to your new video card?
*If your system was using built-in video, did you disable it correctly?—If you need to manually disable built-in video and didn't do so first, your old and new video are fighting over who's in charge. Guess what? You lose.
*Make sure you don't have a bare wire or screw touching the motherboard or any cards—A short stops the system in its tracks.
*Check again—If you had to move or unplug and reattach any power or data cables to perform the upgrade, make sure you properly reattached everything.
Basically check in the Bios that AGP is set as the default for graphics and make sure you have checked ALL leads and connections again. Sometimes the card may not be seated correctly. Also, be careful of static.
Good luck and tell us how you go.