Maybe the system is locked after an incorrect code has been entered into it.
Leave the system powered-on for 1 hour. Normally, it will reset after 32 minutes. If it does not, turn it off and back on.
If this does not resolve the problem, try holding the "BND" (BAND) button, it should allow you to enter the code. If it says "----" and you can't enter the code, leave it powered-on again, it should change to 0000.
A.R.S., January 2013