Why does my tv turn off by itself after a half hour?

When I turn on my 17" lcd tv, there is a very distorted picture but it resolves over next half hour?

• Areas of flat colour seem to be unaffected i.e. menu screens. Most noticeable when picture shaded or dark. Looks as if these areas of the screen are "fizzing". No one part of the screen as it moves with the picture. As I said, it suddenly clears 10 - 30 mins after turning it on and then is ok for the rest of the time. It was fine when I first bought it a couple of months ago. Any ideas what is going on, will it get worse and should I take it back to the shop, ps it is DMTech, from Currys

• Answer:

  It's faulty call Curry's Support if it is still under warranty. I think they are called Mastercare.