nstalled airport extreme and now no video
I plugged the hard drive back in and restarted. The computer restarted normally, full video, fans working normally, everything is fine. I shut down again, plugged the optical drive back in and restarted. The computer seems to be working normally again. I have no idea what went wrong.
I want to thank everyone for their help and especially Jimmy Greystone for advising me to unplug as much as I could and then restart. That seems to have done the trick.