Resetting a Cisco ASA 5510 to Factory Defaults

1. Connect your console cable and make sure you can see the command prompt for the ASA. 
2. Power cycle the appliance – flick the power switch on the front off and on again. 
3. Watch the boot progress, and when prompted, press Esc to interrupt the boot and enter ROM Monitor mode. you should now see the rommon prompt: 
rommon #0>
4. Enter the confreg command to view the current Configuration Register setting: 
rommon #0> confreg
5. The appliance will most probably have the default Configuration Register setting of 0×01. Answer no when it asks you if you want to change the Configuration Register setting. 
6. Change the Configuration Register to 0×41, which causes the appliance to bypass its saved config at boot: 
rommon #1> confreg 0×41
7. Reboot the appliance with the boot command: 
rommon #2> boot
8. The appliance bypasses its startup configuration. When it finishes booting, you should see the default prompt: 
ciscoasa>
9. Enter the enable command to enter Privileged Mode. The default password is blank, so when the appliance prompts you for a password, simply press return: 
ciscoasa> enable
10. Erase the startup config by issuing the write erase command: 
ciscoasa# write erase
11. Enter Configuration Mode: 
ciscoasa# configure terminal
12. Reset the Configuration Register to the default of 0×01: 
ciscoasa(config)# config-register 0×01
13. Exit from Configuration mode: 
ciscoasa(config)# exit
14. Verify the Configuration Register settings by issuing the Show Version command: 
ciscoasa# show version
15. At the bottom of the output, you should see the Configuration Register settings:Configuration register is 0×41 (will be 0×1 at next reload) 
16. Save the settings by issuing the write command: 
ciscoasa# write
17. Reboot the appliance: 
ciscoasa# reload
18. When the appliance reboots, it will have a basic factory default configuration, with a blank password.