2000 witrh 2.7 engine stalls and won't restart

2000 Intrepid. 2.7 liter.

Battery light went on over the weekend.
Able to turn on and off in driveway and drive it around.
Finally lost electricity.
Tunred off and would not restart.
Had alternator changed. Battery checked and O.K.

Daughter drives it to college.
2 days later battery light on again.
The mechanic she saw says its probably the computer and quotes $500.