How can i tell if the computer is bad?

What is your question?

1 the side mirrors move on there own. 2 alternator gauge & oil gauge move at random. 3 I changed the alternator it still shows charging then drops below 12 volts when you stop at a light some times. 4 the wipers also move on there own every now and then. I'm thinking it could be On Star ? 5

How long has your 2002 Chevrolet Trailblazer had this problem?

Only had car two weeks got it from brother