SuperMac cards must be configured for the specific display they are connected to. If you move the card to a different slot in your Macintosh, connect a different monitor to it, or reset PRAM, you need to reconfigure the card to output the proper signals and timings required by your display.
How To Reconfigure
1. Hold down the Option key on your keyboard at startup.
2. Release the Option key when the "Round Robin" configuration cycle begins.
3. When you see an image of a keyboard, on your screen, that is clear, centered, and at the resolution you want to use, press the Space bar. The computer restarts, and the card and display should now be properly configured.