2003 Xterra - won't start

Had issues with my car starting yesterday morning, a little sluggish. Went out & made 3 stops - each start was a little worse & on the 3rd attempt it wouldn't start at all. Tried jump start - nothing. Called for a tow, he tried jumping - still nothing. He even crawled under it & tapped the starter while I tried starting it. Made a little difference but still wouldn't start. Replaced the starter today & now it clicks once & nothing else happens. Tried jumping again - nothing atl happens there. Don't know what to look for now. Didn't see any fuses with issues. Battery? Alternator? Light a fire under it?
I'd appreciate any suggestions..
Thanks