Why is my Philips TV click off & on whle watching?

My Philips tv is around 7 Yrs old. While watching it, it clicks off & on, and finally clicks to no picture or sound. ( it's a clicking noise it makes when it happens) The power to the tv stays on, with no picture or sound. After I turn it off and wait a little bit, i can turn it back on, and the sound & pic are ok. It does it so much now, I can hardly watch it. What would be causing the problem?