What may be wrong with my tv?

My 27 inch Philips Magnavox color TV turns on with sound and will stay on but instead of a picture it has a rainbow colored screen and the little green light flashes fast by the on button behind the little window it's in. The TV is 6 yrs.old - Model#TS2744 C103. Serial#20011694.Chassis model #27B800-7562.Could you tell me what may be the problem and is it worth fixing?