This could be a fault in the TV itself or something as simple as a stuck button in the TV Front Panel or the Remote Control telling the TV to constantly turn on turn off. Start by taking the batteries out of the remote, and try turn it on with the Front Panel buttons. Give the buttons a hard bang to unstick them if that's the problem. Other than that, bring it to a repair shop.
quick tip: post make and model number and state tv type - crt, lcd, palsma... - if you expect any useful help.
In my experience, this usually means the set 's power supply is in protection mode; unless experienced your chances of troubleshooting and solving this yourself are slim to none. see what the tech says...