My Sony LCD rear projection tv is 3 yrs old. It will turn on and then kicks off every minute and a half and then comes back on and continues to do this non-stop. I would like to know the problem

Because Sony LCD rear-projection TVs tend to be larger than other televisions,they are more susceptible to overheating after long periods of use.This is especially true as your television ages. To prevent this,ensure that nothing covers the air vent on the back of the unit. Also,make sure there is no item that generates heat (e.g., a fireplace, afurnace) near the TV. If your TV begins to overheat, it will shutitself off randomly during use. If this happens, leave your TV off fora few hours before attempting to use it again.
if ur unit is not under any extended warranty we would advice you to check the power supply board in ur tv and check for any blown cap..... or some loose solder connections... please exercise utmost caution while ur checking the internal boards .... make sure u take all safety precautions as these tvs are known for their voltages..... using a ohm metre test for continuity in the board to locate the faulty component....
if you are not comfortable doing such a work... i would advice you to take a professional help....
regards iversh