When I turn on the power the TV makes a double click and doesn't go on. I sometimes have to turn it on and off repeatedly for up to 20 minutes before it stays on

The double-click is most likely the TV turning on, then off right away. This could be any number of problems. If you just recently purchased the TV, exchange it. Otherwise see if it's under warranty and either call Panasonic to look into repair, or the place you purchased it from (if they service under the manufacturer's warranty or you purchased an extra warranty from them).

DO NOT TAKE THE TV APART YOURSELF. I cannot stress that enough. Let someone who knows what they're doing take it apart.