Pontiac Firebird 1967-2002 - Need help ASAP

On my 99 trans am my head unit keeps going off and on then stays off but when it stays off the power windows don't not work. I called the gm shop in town they said it would be 120 to run the test. If anyone had this problem any help will be greatful

Your alternator went bad. Go to the junk yard to get one. Just go down to autozone to make sure it's not your battery, but it sounds like its your alternator