This sounds like a problem I ran into with the Radeon 9200 in OS 8/9. It happened when I reset PRAM or significantly changed configurations. No video would come up and I never figured out why.
Try starting up and just let it run for a few minutes, that should be enough to complete the boot cycle. Then press the power key on the keyboard and hit return. This should shut it down. If that doesn't work, just turn off the power manually. Then turn things on again. You should get video.
If by chance that still doesn't work, go back to the built-in video or an older video card if you have one. If it then works, it's something with the 7000 that your system doesn't like.
Try starting up and just let it run for a few minutes, that should be enough to complete the boot cycle. Then press the power key on the keyboard and hit return. This should shut it down. If that doesn't work, just turn off the power manually. Then turn things on again. You should get video.
If by chance that still doesn't work, go back to the built-in video or an older video card if you have one. If it then works, it's something with the 7000 that your system doesn't like.