[Rns 315 power button]

Called a vw dealership they quoted £110 just to have a look ,I think the problem is the actual power button, but at the moment it's on all the time but goes off with the ignition, but if I take it to bits it might never work again. 

[Rns 315 power button]

Over the past few day my rns 315 will not turn on ,it has the time display in the middle, today I tried again and it worked  but now I'm unable to turn it off with the power button ,I'm guessing this is the fault, any ideas please.