Reset 3com baseline switch 2924 - 3Com Baseline 2924 24-Port Gigabit Ethernet Switch (3CBLSG24)

A very simple solution to r epairing all by yourself is getting help from handbooks, they're very detailed and complete in every way so for me it was my b est source to repair
one of the top sites for this is https://big-manuals.com/

Connect the console cable, open a connection to the serial port via a utility such as PuTTY, and do the following:
1) Enter the user name "recover" and password "recover" to place your unit in password recovery mode. The unit will remain in password recovery mode for 30 seconds max.
2) Perform a hard reset by removing power, waiting 10 seconds, and then re-applying power.
3) Once the switch has rebooted, enter a new password for the "admin" user account.
4) Enter enable to leave password recovery enabled, or enter disable to turn it off. You are now logged in as the default "admin" user.
Note: If password recovery has been disabled, the only way to recover access is to return the switch to 3com.

To re-enable the Console access requires the SW2900 series to be reset to its default settings via the WEB INTERFACE
- Web Interface
- Device >Configuration >Initialize To change the Default User "ADMIN" password it is necessary to use the Console connection
-Console Interface
-Once the unit has successfully booted and the prompt presented
-Enter "password" (without "")
-Enter "admin" when the system prompts for User
-Press the "Enter" key when the system prompts for "Old Password" (the ADMIN password was reset by the Web Interface commands)
-Enter "" when the system prompts for the New Password (where "" is the new product ADMIN password)
-Enter "" when the system prompts to confirm the New Password In order to complete the configuration it is necessary to save the configuration via the WEB INTERFACE
-Web Interface
-Device > Configuration > Save
Symptom:
SW2900 Baseline Switch - Default console access disabled following password change
From the web interface, the default user "admin" password is changed and console access is disabled
Cause:
When applying the new password, by default the service-type is set to "telnet". When applied, the default "terminal" setting is removed thus disabling console access.

Power it down for a few minutes and try it again

First,"There is usually a small button on routers that can be accessed with the tip of a pen or a paperclip. When you find that tiny button, hold your pen or paperclip down on it for approximately 10 seconds until the router resets itself to factory defaults."
After that, you can contact the manufacturer to get some helps if you still have problem.

BTW,
I work for Ingellen Communication Equipment and we are a large fiber optic equipments manufacturer in Shenzhen.Kindly let me know your specific requirements so that i can help

If it's the Power Plus (3C16475BS) model, there should be a reset button inside a small hole on the back. "10 - Recovery Button" Inserting a paperclip or similar to reset. If it's not the Power Plus model and is in fact (3C16475A), this is an unmanaged switch, with no administrative capabilities. You don't need a password.
http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase&sku=3C16475BS

Manual can be found at the following web site:
http://support.3com.com/infodeli/tools/switches/baseline/3Com_Baseline-Switch-2916-2924_User-Guide.pdf

you can refer the user guide

http://support.3com.com/infodeli/tools/switches/baseline/3Com_Baseline-Switch-2916-2924_User-Guide.pdf

page 22 of the 3com user guide for your switch talks about how to use the console cable and how to connect to your pc, I included the link below for your manual, if you don't have it:

http://support.3com.com/infodeli/tools/switches/baseline/3Com_Baseline-Switch-2916-2924_User-Guide.pdf