Wow, not much to go on so far.
What's the model number of the set?
Did you check the fuse first?
It SOUNDS like you've got power to the on/off function, and you may very well have a
power supply problem, but it's hard to know what to look for with so little information.
Be warned however. When you give us the Model Number of the set, you'll be getting
all kinds of suggestions about what to try to check.
Are you electrically inclined, do you have some electronics background, do you feel
comfortable working on the insides of your TV?