Today I have been overhauling my home network and generally cleaning things up. The config on my Cisco ASA was ancient and it had loads of stale configuration on it, so I decided to blow it away and start fresh. The following commands can be used to reset an ASA, it effectively changes the boot sequence to ignore the startup configuration file, this allows you to erase the existing configuration from the console. I have found the physical reset button on the back of the device does not actually work.
1. Break the boot sequence (any key when the device is starting)
2. View the conf reg (boot sequence) type confreg
If you confreg is set to 0x1 that means the ASA is looking to the startup config, which is normal.
3. Change the confreg to 0x41 type confreg 0x41
4. Type boot
5. Type enable
6. Type write erase
7. Type config t
8. Type config-register 0x01
9. Type exit
10. Type write