i got 10.1 on Saturday from Comp USA, and came home to install it over my 10.0.4 install. it took forever, but seemed to work ok. I logged into my existing account, and opened the System Prefs to change the monitor settings to 1600x1200, which is the resolution i prefer. i guess i accidentally selected 1600x1200 @85Hz, because it kicked me into the monitor's "Out of Scan Range" screen. In earlier versions of the Mac OS, holding down the mouse button would bring back the previous setting. not so in OS X.
i could no longer use OS X, because it kept booting the computer up in an invalid range and i couldn't see the OS to change the resolution. The mac has handled this kind of thing far more elegantly than Windows for at least a decade - to revert to this kind of unintuitive behavior is just inexcusable.
in any case, i could not do a thing to make this work. zapping the PRAM no longer resets the monitor values to a default like 640x480, and disconnecting the monitor, shutting down, booting, shutting down, plugging in the monitor and booting didn't do it either. After asking around on another BBS, i was able to get the system back. deleting the file:
/Library/Preferences/com.apple.windowserver.plist
while in 9.2 and rebooting into X worked fine. It inherited the settings from 9.2, and i'm now working from 10.1 again.
-perry
December 20 2001 Update: An alternative method of solving this problem is to restart with the shift key down during a reboot - this seems to now indicate to OS X "reset the monitor at startup" instead of "disable extensions". This solution courtesy of this thread on the MacNN forums.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2001100114532165