From Password Recovery Procedure for the Cisco 2600 and 2800 Series Routers.
minicom
After making sure you have done all of the above steps:
Password reset works when the device is powering up, but we have to do something special before powering on.
Readonly ROMMON initialized rommon 1 >
confreg 0x2142
reset
Press RETURN to get started!
Press the Enter key, and you should eventually see:
Router>
enable
You should then see:
Router#
copy start run
If it prompts you for running-config, press Enter to accept.
show run
config t
enable secret cisco
end
Messages may appear unsolicited after that; press Enter to see the prompt again.
show ip interf brief
For example, if only FastEthernet0/0 is showing down:
config t interface FastEthernet0/0 no shutdown end
config t config-register 0x2102
end
copy run start
reload