Here is one from the history books. How to factory reset a Nortel 5510/5520 switch when you don't have IP or serial access to the device.  This situation does occur (forgotten password on device manager, web access or console access for example).

The process is as follows:

1. Press and hold the UI button for 3 seconds, the unit will be in configuration mode and the status light will change to a blinking green status.
2. Press the UI button 5 times, the base led and up and down leds will now be blinking amber and in unison
3. Press the UI button and hold for 3 seconds to confirm the command.
4. The in use IP address will now be 192.168.1.168 and you can access it via  device manager, a browser or via the serial port. Best to check this IP with wireshark as I am running from memory, but you can always use a console cable to set via the serial port at this point.

Since we are on topic here are some other options for a factory reset on the 5500 range (and other Nortel switches)

Via the console port follow these steps:

1. Connect to the console port of the switch (9600,8,N,1) with putty
2. Reboot the switch.
3. When the first line of the diagnostics tests is displayed, press CTRL-C. The system then displays a menu.
4. Select option “i” to factory default the switch.
5. Select option “a” to run the agent code.

Upon boot up, the switch will be in a factory default configuration.

Via TFTP try this: Presumptions....

• You still have SNMP-access
• The software agent allows downloading the ASCII config of the switch to TFTP

1. With device manager instruct the switch to put the ASCII config on your TFTP
2. Edit the line for the telnet/console password en set it to ‘none’
3. Save the config file
4. Upload it to the switch
5. Result will be that you can login without password and be able to set a new password.

Attached is a link to the Nortel 5500 configuration reference guide..

5500 Series Config Guide