If you do not know the password, default "Cisco" then you must bypass the config and enter a new one, you could try the below:-
Step 0. Plug console cable in.
Step 1. Power cycle the device
Step 2. Send a "break" command to the device within the first 60 seconds after power cycle. Hit "Control /Break"
Step 3. From the ROM monitor prompt, set the configuration register value to 0x142. This causes the device to bypass the configuration contents stored in NVRAM upon next bootup. To do this, type:
> confreg 0x142
Step 4. Once the configuration register has been changed, initialize and reboot the device by typing the following:
> reset
The device will reboot itself.
Step 5. After the device boots up, you will be prompted if you want to enter the initial configuration dialog. Type: "n" for no. Note: If you accidentally enter the initial configuration dialog, abort by typing: .
Step 6. Enter privileged EXEC mode by typing the enable command. No password will be required. The prompt will change to device(boot)#.
device> enable
device#
Step 7. Load the original configuration back into the device.
device# copy startup-config running-config
Note: If the device has originally been configured with a hostname, the prompt will now change to device_name#
Step 8. Set the new enable password.
device# config term
device(config)# enable secret
Step 9. Restore the configuration register and exit configuration mode.The configuration register must be reset so the device will properly boot using the configuration now stored in NVRAM.
device(config)# config-reg 0x2102
device(config)# end
Step 10. Save changes
device# copy running-config startup-config
Step 11. Reload the device
device# reload
Before doing this I would recomment that you try and find out the enable password!
HTH.
