Will not start on 2004 Cadillac CTS

My car will not start. I drive it and it is fine then when I go back to start it again...nothing. No lights, sounds, power...nothing. Then it will start again for whatever reason and run for days. All of a sudden it's in a coma again and is revived after just seconds on its own. WHY?

Asked by for the 2004 Cadillac CTS
check and clean the battery cable connections to start.