voless

I have an 05 Chevy Silverado. Last week I noticed the clock was resetting after everytime I shut it off. Just now today when I went to start it and it just clicked like the battery was dead. Tried it again and it started right up and drove fine for a 100 plus miles. Next time it did it again and eventually started again. SOmetimes when I turn the key I get nothing no radio, insturment panel, then other times those things work but I get the dead batt. click. I noticed if I shut the drivers side door with some decent force the instrument panel and radio will work. I'm sure its a wire but where do I start.