I had bought 2 cisco 2950 switches for my education. The guy who sell them to me told me he had lost the passwords. So i started looking for a hard reset.
In the following instructions I am going to reset the switch to defaults:
Step 1: boot the switch and hold the mode button.
Release the Mode button after approximately 5 seconds when the Status (STAT) LED goes out. When you release the Mode button, the SYST LED blinks amber.
Step 2: The switch boots and the following screen is displayed.
Step 3: Type flash_init
Step 4: Type load_helper
Step 5: Type dir flash:
Step 6: rename flash:config.text flash:config.old
Step 7: type boot
Step 8: after booting type enable (you are in !!!!)
Step 9:Type rename flash:config.old flash:config.text (to restore the original settings)
Step 10: To make the changes written to running-config
type: copy flash:config.text system:running-config
Step 11:you now see the original hostname of the switch. The only thing that is left is changing all passwords.
Step 12: change secret password:
conf t
enable secret custom_password
Step 13: change cleartext password:
enable password custom_password
Step 14: configure passwords for ssh and console
for console
line con 0
password custom_password
login
for ssh
line vty 0 15
password custom_password
login
official cisco article: http://www.cisco.com/en/US/products/hw/switches/ps628/products_password_recovery09186a0080094184.shtml