Maybe your new battery is dead or needs a charge before using.
The same way you started it before replacing the battery.
Does it turnover?
No
battery may not be the problem check your starter motor and ignition switch
did you unhook the battery before replacing the alternator
Start by replacing the battery in the remote.
You need to replaced the starter or the alternator.
try replacing your battery maybe turn the key?
Clean battery terminals, then tighten down the battery cables. With the ignition key---like any other time.
Is starter working?
Battery is dead.
You can hook the battery charger to the battery in the trunk, or to the jump start posts under the hood.