If I'm understanding you right.
It was working fine then just went dead, now you get no indication of power at all, right?
Do you have a test light?
If you do clip one side to the battery pos and then touch the frame/body/engine, light should light.
Now go to the starter and clip to the large stud that the battery wire connects to, then touch the starter case, light should light.
Now look at the large stud and you will see another wire attached, follow it till you find a fuse check that fuse.
check back after that.
And No, a bad alternator will not cause your completely dead issue with a new battery.