I change my battery and alternator and battery still won't charge

Do a simple test by toughing a screw driver to the back of the alternator, if the screwdriver holds on the back of the alternator it's charging,if it doesn't your regulator inside the alternator no good.

If You have a new battery and alternator do the following. Make sure the wiring is ok and the terminals are shiny clean, make sure the battery is fully charged, if the voltage drops below 10 volts when cranking the computer wont work, does the charging light on the dash light up with the ignition on, If not The alternator wont charge because it needs a voltage feed back through that circuit to charge . some alternators have a external voltage regulator check this also.

You out the alternator in incorrectly. please triple check the installation of the alternator.