when turned on there is no sound or picture and then the tv turns off?

We have a philips 37" ambilght lcd (mod. no. 37pf9731d). The 'on - off' button on the tv broke some 3 months ago so the tv is always turned on via the remote control from standby. Today when the plug in the wall was turned on, the tv 'on' light was green and never switched to red (standby) as it normally would, a click was heard after 30 secs or so and although the green light stayed on there was no picture or sound even when we were pressing 'on' on the remote control. Also, when first turned on at the wall the tv will play a DVD (picture but no sound) until the click is heard and then the picture disappears again.

What is the problem?