Help me stop Rooted Android Boot Loop?

I have the Motorola Droid. It is rooted. It is currently in an endless pattern of freezing, shutting down, and rebooting. The "holding down 'x' " technique does not work. I don't know what to do after holding down the upper part of the D-Pad. I still don't really understand what flashing a ROM means. I don't understand how to follow others' instructions when it must be performed on a phone that is not constantly rebooting itself! Please help...with step by step instructions for the newbie!