To check the fuse, take it out and look through the glass to see if there's a filament intact inside. If it needs to be replaced, look at the metal end caps. There is usually a value etched there. It's easy enough to take it with you to Radio Shack to get a replacement.
One more thought on fuses, I have on rare occasions had a fuse that went bad, but looked just fine. Also if the fuse is not seated securely in it's clamp holder it can break the signal path.
The screws are on the crossover network. They are nestled in the barrier strip. Sometimes the contacts will corrode enough to degrade the signal. Just loosen each one, squiggle or remove and replace the spade connector. Tighten it up. It is surprising how many times this is the issue.
If the woofer is bad, Bob Crites, (BEC) on this forum, is an excellent source. You can get a replacement for about $100. You may also have run across his parts on Ebay.
"I know I'm paranoid.... but, am I paranoid enough?" --Tom Clancy