This occurs when the captioning feature is turned on somewhere in your system. Here are some steps you can take:
1.Check your television for the "Menu" setting. Select "Screen" (or equivalent). You should have the option of turning captions off. (If you have satellite or cable, turn off the cable box and work directly with the TV to do this.)
2. If this does not resolve your problem, perhaps you have a satellite or cable box with a tuner that overrides the TV's tuner. Call your provider and ask them if this is the case. If they say no, run a test by hooking the cable directly to your TV, bypassing the cable or satellite box. If the captions do not reappear, then it is the cable/satellite box. They should be able to tell you how to reprogram the box to turn off the captioning decoder chip.