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This is how to restore enable password in case that you forgot password..
Send Break message within 60 sec after booting up.
Then changed to ROM MONITOR mode.
(Cisco 800 series does not have ROMMON mode, but boot# mode.)
boot# set
set baud =9600
set data-bits =8
set parity =none
set stop-bits =1
set console-flags =0
set mac-address =0050.7307.C329
set unit-ip =10.200.40.65
set serv-ip =255.255.255.255
set netmask =255.255.252.0
set gate-ip =10.200.40.1
set pkt-timeout =8
set tftp-timeout =16
set boot-action =flash
set file-name ="c800-nsy6-mw.122-10b.bin"
set watchdog =off
set prompt ="boot"
set ios-conf =0x2102 <<<--- check this value, which will be used later.
boot# set ios-conf = 142
boot# boot
If you are prompted during boot up process, input no.
Router> enable
Then, input password.
Router# configure memory
Register info to memory on router.
Router# show running-config
Then now you can see password.
Router# configure terminal
Router(config)# enable secret password new-password
or
Router(config)# enable password new-password
Router(config)# config-register 0x2102
Input ios-conf value which was shown previously with command set or input 0x2102.
Router(config)# exit or Ctrl+Z
Router# write memory
or
Router# copy startup-config running-config
Router# reload
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Reference
http://www.cisco.com/JP/support/public/ht/tac/100/1008567/pswdrec_800-j.shtml
http://www.cisco.com/JP/support/public/ht/tac/100/1008554/index-j.shtml