I have forgot my admin password in 3com switch 4500 could you please help me

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.

Username:monitor Password: monitor---monitor mode, view only manager manager--can change all except security features admin (no password)--sets security features IP: 169.254.100.100 or 169.254.100.99

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

Please try with the below combination of passwords for 3com Router

synnet
tech
(none)
admin
ILMI
PASSWORD
adminttd
comcomcom
security

if you havnt changed the password to the router then it should either be "PASSWORD" "ADMIN" "ADMINASTRATOR" in the worst case senreio you may have to reset the router.

not sure about the 3COM side, but on the Cisco side... go to the configure prompt, then the port that you need to trunk (int [interface name and number] and enter)

Once you are in the interface, use the following command:
switchport trunk encap dot1q
switchport mode trunk

Then make sure that the interface is not shut down, connect the switches together and (hopefully) the 3COM will negotiate to trunking... if not you will need to manually configure the 3com.

Hope that this helps!

You forget the password for the "admin" user account and can no longer perform important management operations. Use the password recovery method outlined below to define a new password for the "admin" user account:

1. Access the Command Line Interface from the console port and enter the user name "recover" and password "recover" to place the Switch in password recovery mode. The Switch remains in password recovery mode for a maximum of 30 seconds, before it returns to the CLI login prompt.
   
   You must use the console port to recover the passsword. If you attempt the recovery method using the network, the password will be rejected.
   
   
2. Perform a hard reset on the Switch whilst it is in password recovery mode by switching it off, waiting a few seconds, and switching it on again.
   
   You cannot use a soft reset operation to reset the password of the "admin" user account. This will end the password recovery procedure and return you to the CLI login prompt.
   
   
3. When the Switch has rebooted following the hard reset enter a new password for the "admin" user account.
   

i can't set ip address over 4 vlans. the 3com switch 4500 always give error message "there's not enough routing resources available".please help....