system folder will NOT boot


i was using 9.2.1 and i went to the startup disk pref panel and selected 10.1...when i restarted my computer, the system folder thing flashed between a question mark and the mac face.
i modified nothing in either my 10.1 or 9.2.1 system folders.
when i put in my 9.2.1 install disk, it works.
if i try to restart into either 9.2.1 or 10.1 now, nothing happens....just the blinking face and question mark.
does anyone have any ideas about what is going on????

Holding down option should at least let you get back to you OS 9 install... although I don't know of a way to "fix" a broken OS X install from the OS 9 finder...
I'd love to hear if anyone has any ideas on how to do that.