Why does my TV flick on and off standby on its own?

My TV is a 42" Widescreen HD Plasma.

When the TV has been on for a while it suddenley flicks to a white light as if in standby and tries to turn on again but doesnt. It flicks the standby on and off making a clicking sound.
It doesnt actually go into standby or turn on it clicks inbetween the two.
There is nothing on the screen when this is happening.