faulty standby light?

My Palsonic flat screen TV's Red Standby light wont turn to Green.
Some days it does and goes for days or a week.
But just recently it hasnt.
It has been going out at an average of 3 to 4 times a week with nothing but a black screen for those days.
Then when you least expect it, it comes back off
standby onto green and can go on for days until next time.
so whats the problem