I recently had a problem in my home lab where I had forgotten the password to my 3COM 2928 SFP Plus switch. So I was unable to logon to the web administration page to configure the ports.
 
As I understand it, if you do not know any usernames/passwords for the switch your only option is to perform a factory reset, losing ALL configuration from the switch. So hopefully you have an up-to-date backup of the config to re-apply, or it was a simply setup you can remember. You need to do this out of hours if it's in production!
 
Note: The default password for a 3COM 2928 SFP (I assume its the same all the 2900 series and some other 3COM switches):
 

Username: admin
Password:  

 
 

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