I lost my display a couple of times as well since Tiger due to out-of-scan problems. The solution is easy: In the /Users/<Username>/Library/Preferences/ByHost-directory of the user who changed the resolution you should delete the file that starts with com.apple.windowserver.plist (behind that is some code to identify your computer, in case you have a network home directory.

You could delete this file from from single-user mode, an admin-account, from OS9, whatever you feel comfortable with.

And in my case: I have an LCD (Eizo L557) and merely clicking on the selected resolution (1280x1024) makes the scan frequency go crazy, without a warning dialogue. Even though it is connected through DVI. Very strange, but I think it is just a 10.4.0-thing, will be fixed soon.

You may also be able to bypass the scan rate problem, and delete the windowserver.plist file, by starting up the Mac in Safe Boot mode (hold down the Shift key at startup).