Fansite SnootySims has in the past discovered several cheats for the Sims 2, and recently they found another one. With it, you can set the volume of the TV. Press and hold Control and Shift, then press C and release all buttons to make the cheat bar pop up in the game. Then enter "floatProp tvVolume" (without quotes) followed by a number from 0 to 1 (with several digits). The value of 0.5 is the default volume for the tv, so for example you can enter "floatProp tvVolume 0.5" to reset the volume.