Make sure it is plugged into a good electrical circuit and turned on. Ensure the TV is programmed to match the input connections you are using, cable, satellite, HDMI, etc. If whatever method you are using requires the TV to scan for channels/stations, run the scan. If these and everything else fail, call the Best Buy Geek Squad.
What exactly is wrong with it? Some general troubleshooting tactics are unplugging the television for a few minutes and then plugging it back it. check to see it any lighted ares of the tv are on (such as the power light, stanby, etc. )Try switching power outlets, possible in a different room.