Big screen tv broken
If you're NOT still under warrantee you should at least open the TV and look for a blown fuse near where the power cable enters the set. A lot of times you can buy replacement fuses at a local electronic or hardware store and they're easy to replace.
Check the fuse. If it is blown, it will be obvious and make sure that the set is unplugged before replacing it. If it blows again, or if it is not blown, your problem is probably in the 'X' volt regulator and you will need professional help with the repairs.
You can also check the board where the components are mounted and resoled any that look bad. Brief power outages may cause the TV to turn off on its own. If you are using a surge protector, try connecting the set directly to the wall outlet.
In your case it could caused by a blown fuse, a leaky diodes or a bad solder joint at the horizontal drive transformer.
All can be replaced at a local electronic or hardware store and they're easy to replace
If this does not correct the problem, you may need to have your TV serviced.