This happen to me also, Was playing around with the radio, and during this i disconnected the power cable to the unit.
after putting this back I coundn't remember the password I put in a couple of weeks ago
after finally got to read the following file I was pissed of the password that I had entered. I was trying for 4 digits but instead it was bday date.
correct location is USER\SYSTEM\SECURITY\PASSWORD.DAT
EDIT that file and you will see the password