Have you checked your battery? A easy check is to measure it voltage but the most definitive test is a load test which many auto parts stores will do for free.
If the fuses blew when you were changing the alternator it sounds like something got shorted which could mean there are other problems.
Can you describe what happens when you turn the key, I'm guessing nothing?
you say don't start but does it turn over?
if no crank and if battery is good (yeah test it) positive you did short something and kill the new 40A slow blow that protects main circuit?
that one gives you same symptoms you are seeing now.
if it does crank ignore this.