If you are trying to configure a Cisco Router, but a password is blocking you from enable mode, follow the steps below to reset the password.
Download a program called Putty from the first resource site below. PuTTY is a terminal emulator application which can act as a client for the SSH, Telnet, rlogin, and raw TCP computing protocols (Putty on Wikipedia).
Connect one end of the blue serial cable to the Cisco Router and the other to your computer. Open up the Putty program on your computer and select the radio button next to “serial” on the right-hand side of the start window. Click on the “Open” button in the bottom right-hand corner of the Putty start window to open the terminal.
Power the Cisco Router on. As soon as the router begins loading in the green and black Putty terminal window, press the “Ctrl” and “Break” keys simultaneously until its going into rommon mode.
Once in rommon mode, you have to change the configuration register number to make the router boot from a blank configuration file. For the 2800 series Cisco Routers, the command “confreq 0×2142″, changing the register number to 2142, worked. Search on cisco.com for information on your particular Cisco Router Series.
Type the restart command in rommon mode, which is “reset”. This will boot the router up again. When it is finished, you should be able to type “en” to get into enable mode without a password.
Once you change the running-config in RAM and save it to the startup-config in NVRAM, remember to change the configuration register number back to its default (usually 0×2102). This is important if you change anything on the running-config. Thanks for reading