screen resolution

I’am using a 19″ TV on my P.C. and i cannot alter my screen resolution because when i do alter it it gives one “x” seconds before reverting back to what it was. my problem is the screen goes black for longer “x” seconds so i cannot tick accept before it reverts back to what it was. Question: does anyone know how i can alter/extend the amount of seconds before it reverts back to what it was. thanks