I had the same problem to fix it you press the menu button then scrool up untill you see REGISTER.
Press OK the display shows "BS 1 2 3 4" Enter the number of the base unit you wish to register the handset to.
The display shows "PIN code" (original code 0000) press OK the display shows "Search X (where 'X' is the number of the base you are registering to)
Press and hold the "page button" on the Base unit untill it beeps twice then after a few seconds the phone should work again.
http://go.to/mrm
(The site above has the Maunal for your phone if you need any more help this should help)
Ste, August 2006