Picture too dark

You didn't say if you are receiving an off air picture or cable or satellite. The reason the commercials look good is because the local station (or source) transmits them "in the clear", that is, without any enhancements to the video signal. Network programing or local newscasts are sent through a device which inserts a reference signal in what's called the "vertical interval". You may have seen this as a series of flashing dots or pulses at the very top of the picture. There's a lot of information packed into the VITS (Vertcal Interval Test Signal). One of the lines contains a reference pulse for video which is set at a certain level. Your TV sees that level and automatically adjusts its circuitry accordingly. What I suspect is that your set is out of calibration and is pushing down the video signal because it is not "seeing" the level properly. A video alignment should correct this and can be done by a good repair facility. Hope this helps.