The only fuses that the amp should have is one on its main power line that goes directly to the battery(typically this cable is red or blue in color), and the ones that are on the amp itself. The fuse that is on the main power line, is that a tube shaped glass fuse (AGU)? Or is it a maxi blade type? Well, if it is the glass type, they are notorious for looking intact, but actually being defective.
The solder connection that is made internally gets weak and no longer makes the connection from within the fuse. So the metal strip on the inside looks as if it is fine, but the fuse still conducts no current. If the fuse is in fact %100 fine, then my next question to you is; do you have multi/voltmeter? And do you know how to use it? We can continue with the trouble shoot if you answered yes to atleast the first question.