I have a LCD monitor wwhich can be used as a TV too. I have been using it for around 3yrs. The TV has 5 source modes TV, SV, AV, YPbPr, VGA. This morning when I turned it on, it started switching modes automatically, staying at one mode for a few seconds. While it is auto switching mopdes, I cannot manually change the modes either. Thus making the TV/Monitor unusable. Any ideas what's ailing my monitor? I will be taking it to a repair shop soon.
My Samsung 23.6" does the same thing. It happens when it can't detect the source input. When it happens, it switches to the next mode looking for a signal. It stops when an input signal is detected.
So in your case I assume you checked that all the connectors are in place securely. If it is then there's something wrong with the tv itself.