1999 Mercury Mystique Car won't start

My car won't start, it won't even crank. The lights work, the dash lights up but it just clicks and nothing. I have had this problem before, got a new battery. Basically it will start one day and not start the next. I have no idea when it will or will not start. This has happened 4 times in the last 6 months. The first 3 times I got a jump and it was fine. This time when trying to jump it did nothing.