All of my warning lights are on

All of my warning lights are on in my 2004 pontiac sunfire it has a good battery in it, but sometimes it will turn over and then die. I don't know what's wrong with it; I have taken it to several shops and at those times they used some type of machine to check it but nothing yet is found.

It takes a while to crank sometimes it turns over then dies, and once its running the warning lights are on including the theft light which makes it hard to put the car in gear and once I reach my destination I have to pop the hood and loosen the battery just enough and tighten it back so that the head lights will go off because they don't go off when I switch the car off. Also if I drive the car one day and drive it the next the car will not do anything; meaning that some how the battery dies which causes me to get it recharged. I have had my battery checked and it has been listed as a good battery. nice site :-)