1999 Nissan Maxima Starting problem

My daughter recently bought a '99 Nissan Maxima and it was fine for a few weeks but then one day when she dropped it off to be detailed, the worker could not get it started. The following day he said it was a starter problem, replaced the starter and it was fine for a few days. Then she couldn't get it started again. I showed up and it started OK. Two days later, Saturday, she was stranded again and this time I could not start it. Tow truck driver could not start it and he took it to another repairman. Monday morning it starts OK for the repairman, he keeps it for a few days and cannot duplicate the problem. My daughter picks it up, drives it for three days and now it will not start again. The engine turns over OK, the battery is fine, but nothing happens. Whats the problem?