Cisco ASA Hanging at ROMMON at Boot

After factory defaulting an ASA 5510, we noticed it didn't boot to a default configuration. It booted up to the ROMMON prompt. As soon as you'd type "boot" or "boot device:/filename" it would happily boot for you. Adding a "boot device:/filename" to the config didn't make a difference.

When we did a "show version", the next to last line was:

Configuration register is 0x________

So the trick is to enter the following command:

config-register 0x1

This line sets it to boot the first configuration it finds.

Here is a handy reference URL: http://blog.ipexpert.com/2010/05/27/understanding-the-asa-configuration-register/