On switching on the set - sound ok but no picture

Unless the sound is getting muted and the speaker icon shows with the arrow through it its a main board failure

check the speaker/s. If found OK; check and replace the damaged component/s at its audio output section circuit board. If needy, replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. Surf the site with patience.
http://electronicshelponline.blogspot.com/

Check whether the balance control is settings. Go to the audio menu to both TV and DVD player; and make sure that it is set to Centre position; to both the devices. Still there is no audio with one channel, check it with an other know good disc. Still you can't get sound from one channel, the audio output section to the TV circuit should be checked. Contact any service technician.
Check the speaker/s first. If found OK; check and replace the damaged component/s at its audio output section circuit board. If needy, replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. Surf the site with patience.
http://electronicshelponline.blogspot.com/

A couple of thoughts here--you may have suffered a power loss while away--unplug set for a while and then power back to see if it helps.

As far as the sound it is unlikely but possible the speakers may have got switched off somehow--check in audio or setup menu to see if this is the case.

can you hook up a dvd player? see if you got sound if you do, your TV Tuner is broken

If you can quickly get to menu before picture goes blank, then go picture / backlight / set backlight to minimum and it will work fine.

Problem is your CCD has failed. Expensive repair.

Exact same problem here.

If you have cable and a top of set box , it may be the problem. If you hook the cable direct to the set and still no digital ... then the TV could have a defective digital board. The tuner is on this board and the tuner gets both analog and digital signals.

Perhaps your remote is set to video recorder?  Try that first, and if no response, try calling up a menu on your TV and look for the Picture Settings.
Good Luck.