Panasonic SA-PT460 - Drawer fault - help please!?

My Panasonic SA-PT460 HTS (Home Theatre System) has been faultless for 6+ years.

It has just started playing up. The sound system is still as good as ever. The problem lies with the DVD drawer which opens when the unit is switched on. When I close the drawer using the button on the unit, it just opens again!

I have tried switching off at mains momentarily but no difference - in fact to make sure the drawer is closed when I switch down the power I have to hold the drawer in, (I don't want it remaining open because of dust ingress and the possibility of people walking by catching their leg on the drawer.

Has anyone any idea what the problem is and what would be involved in fixing it?