Please see the regular process to reset the password on 1841 Router below,
- Connect the console cable to Router 1841
- Use the power switch in order to turn off the router, and then turn the router back on
- Press Break on the terminal keyboard within 60 seconds of power up in order to put the router into ROMMON
- Type confreg 0x2142 at the rommon 1> prompt in order to boot from Flash
This step bypasses the startup configuration where the passwords are stored
- Type reset at the rommon 2> prompt.
The router reboots, but ignores the saved configuration.
- Type no after each setup question, or press Ctrl-C in order to skip the initial setup procedure.
- Type enable at the Router> prompt.
- You are in enable mode and should see the Router# prompt
- Type erase start at the Router> prompt.
- Type configure terminal.
- Type config-register #config-register 0x2102
- Type write memory
- Type reload
– See more at: https://supportforums.cisco.com/discussion/11607366/how-reset-cisco-router-1841-password#sthash.keYSGsUX.dpuf