If you need to do a "factory reset" on one of these you can.
- Connect to the console using serial cable.
- Switch on while hitting [FN-CTRL-BREAK]
- (I have a Thinkpad, [FN] not needed on a desktop keyboard). Tricky, may take a few attempts - need to be hitting it really early on in the boot process.
- Get rommon> prompt. [http://www.roadkillnetworks.com/cisco/tftp_rom_monitor_appendc.htm]
- >confreg, >yes, >no to everything except "ignore system config info".
It will then reboot from an alternate configuration file, and you're in! Now however, to clear the existing setup and revert the router to a good state.
- Router#conf t
- Router(config)config-register 0x2102
- Router>write memory