What is wrong with a TV if the power light is on but there is no picture or sound?

Maybe the wire that connects to your T.V. from a DVR or other picture receiver is loose, hooked-off, or not on right.

Also, try jiggling all connections and testing them out individually. Hopefully the screen isn't broken. If it is an older cathode ray tube monitor, the bulb might be broken. If it is a flatscreen, it is probably a circuitry or logic board problem. hopefully, it is just a problem with the wires.