How to Reset Cisco 26xx, 28xx Series Router (Password Recovery) | Cisco

Reboot your router and hold CTR+BREAK sequence to enter into Rommon mode. and enter these 2 commands

rommon 1 > confreg 0x2142
rommon 2 > reset

done :)

Now revert your router sequence back to normal:

Router>enable
Router#config terminal
Router(config)#config-register 0x2102
Router(config)#exit

done:) 

Note: 

last bit of (ox2102) is 2: 
if  2>=0 then it means IOS is loading from Flash. 

2nd last bit of (ox2102) 0: 
If 0 = 0 then , startup configuration is loading from NVRAM.

we change this configuration to no boot from NVRAM, instead bypass NVRAM and with empty settings. by change the 2nd last bit 0 into 4.