Have had the tv a few years now and it has worked great until recently. The tv can be watched with no problems for hours until midnight. After midnight the TV switches off every 5 mins. I have disabled all settings I can see that may cause this and unplugged all except normal ariel and problem persists.
@Velkro: If you go to Menu > System > Eco Solutions, can you check to see if any options here are enabled such as Auto Power Off, and disable them where appropriate to see if this helps? Also, can you go to Menu > System > Time > Sleep Timer, and switch this off where applicable?
If the channel you are on stops broadcasting after midnight, and no signal is being received via your aerial connection, then the TV will automatically turn off.