Laptop screen keeps going black - Please Help

Hi can anyone help? I'm not technically minded at all and need an idiots guide solution if anyone has one.

 The screen on my laptop has suddenly started going dark for no apparent reason. It starts up fine, the desktop comes up and you can see it then suddenly it all goes black. The only way I can get the screen to then display is by pushing the on/off button. When it comes back up sometimes I can use the laptop for up to 10 mins but the screen always goes black again. What can I do?

 Helpless from Birmingham!