We have a 60" HDTV on our livingroom wall. The back of the wall is in the kitchen and has a microwave on that wall. When we open the microwave door. ( not even turning on the microwave yet) the TV will turn off for a second and them come right back on. It started doing this about 5 months ago. And once in a while but not all the time, it will happen when we turn the kitchen light on, which the switch is on a differen wall . Any suggestions as to why this is happening?

Sounds like a brown-out condition. If the microwave and lights are on same circuit, the combined load might be just below an amount which would trip the breaker, but enough to cause sensitive electronics to shut down.

Try to feed the TV from a different circuit and see if problem persists.

This type of condition will greatly reduce the lifespan of sensitive electronics.