sounds like the mains transformer for the light is broken/faulty. They tend not to last long.
(Im assuming its a 12volt two pin spot lamp as its above shower.)
Go in the loft above the shower and unconnect the transformer and replace. (Screw fix direct £5.79)
and it is very easy to do, just unclip the wires and exacly replace as the old one was fitted.
If it is a mains 240v two pin bulb then check the replacement bulb is okay and not faulty.
If all of this fails then just use the main bathroom light to see , or a torch
stupid stuart
November 2008