RCA HDTV My t.v. is 4 yrs old and just recently has started to change channels by itself and when turned off it turns itself back on. After unplugging and letting it sit for a couple of days, it will be o.k. for a couple of hours and then starts the process all over again.

Most probably, you may have problems with your keypad, the keypads are actuall called "tact switches" and they can become "corrupted" or leakey or just stuck, you cant really measure a DC restistance but they can cause all kinds of strange phenomenon such as you describe....if possible, replace the keypad PCB or, if not replace the individual keypads