We’ve have an older 3Com Super Stack II 3900 here in the office. The tech who originally configured it has since left the company and took the administrator password with him. 
Anyone know how to recover the admin password?
Thanks…
The default password for the “admin” account is no password (just press enter when prompted for the password).
If you can not access the switch try the security account using “security” as login and “security” as password. As soon as you gain access to the switch modify the admin account and re-login as administrator. You should avoid to access as security for administrative tasks.
If you still have no access to the switch contact 3Com Technical Support. They can get you fixed.