Phillips 42PF5521d/10 problem

[speccyget]

Hi,
My Pillips 42" Plasma has gone mad. When I turn on the tv the volume automatically turns itself up to maximum. Pressing any buttons on the remote has no effect. When I press either the + or - volume buttons on the side of the set the volume does go down. But, as soon as I release the button the volume climbs back up to maximum again. Any ideas please