I have a problem with my LG LCD tv when cold it will stay on for about 20 mins then goes into stand by.

When you switch it on again it will flicker as the AV channel appears then goes back into stand by has anyone encountered this before, I think it might need a new SSB or PSUs but dont know how to check for this, Idont think it is the screen because i have disconnected it and it still does the same thing, any help would be great because its big and i dont want to skip it. Thanks

I have this with my family's LG plasma, I've found the fastest cure is to pull the power socket and wait for the white light to disappear and the complete power off click, at most a minute.

Can't work out if it's the power supply or the firmware that detects inputs, since it can happen when switching input as well.

Your best bet is to have the input on before firing up the TV, that way it only happens once in a while.  It could be the power supply but I can't be sure...