Thanks very much for the words of wisdom from the people in this forum and your wordsof advice worked.
The stry was I have a compaq laptop thats just over a year old and very rarely used. I went to it ne day and it switched on as normal with fan working, lights ec but blank screen, itried several times and no joy. Phoned pc repair companies and they told me very common fault with these and hp and it was definately the graphic chip that was away, 75 pound to repair, and they were adament it was the chip. To cut a long story short i came accross this forum and read instructions as follwos and hey presto it worked.
TURN OF LAPTOP
REMOVE POWER CORD
HOLD ON BUTTON DOWN FOR 30 SECS (TO DRAIN POWER)
REINSTATE THE POWER CORD AND SWITCH ON
FINGERS CROSSED YOU HAVE A WORKING SCREEN.