Some TV's display a blue screen if there's interruption to the aerial signal & are designed to show a clean blue screen instead of just snow.
Toshiba & Hitachi are two examples of manufacturers using this feature.
Usually the blue screen feature can be switched off from within the TV's user menu. Although you may still have to find the reason for the lost signal.
Check disconnection of power to external equipment eg. video recorder, decoders or aerial amplifiers, as the signal is usually routed through them before reaching the TV.
Otherwise, a blue screen can be due to a fault in the TV.
As simple as a cheap resistor up to a short circuit inside the cathode ray tube, which would be very expensive. Usually but not always, a short circuit inside the tube will be accompanied by flyback lines in the picture (very thin, faint white diagonal lines, spaced about an inch apart).
Check your signal input first.
Cobweb
September 2005
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix televisions.