what would the symptoms of a bad computer be on 2003 Chevrolet Cavalier

My car doesn't recognize my new alternator.It buzzes real low and also my heat gauge and speedometer don't work.

Asked by for the 2003 Chevrolet Cavalier
The car doesn't have to recognize a new alternator, it just needs to see that it is or is not charging. Maybe the new alternator is bad, or another electrical issue.