hi. mine does the same some times. i find a system reset sorts it for a while. u know in the secret menu bit. To access the Installers Menu, use the following set of key presses:
SERVICES, 4, 0, 1, SELECT.
This will give you access to several sections:"new installation" which enables you to reset the system if you are experiencing faults without having to pay someone to come out and repair it! Do use caution though on some other features as it was hidden for a reason.
hope it helps