No sound comes out of the subwoofer. Sound passes through and the power light is on, but no subwoofer sound. Any ideas? Fuse? Easy fix? Can this subwoofer be replaced? is it still available? Can I buy a new one?

This may be a dumb question but have you turned up the signal. there should be a dial on the back that you can turn the power up. power light on, signal passing threw, the only other thing it can be is the built in amp itself may be dead.

There is a Polk Audio Forum here http://forum.polkaudio.com/
Probably a better source of info on your specific speaker. I have a PSW200 which may or may not be similar. Your power light is on, so probably not a fuse. Try turning all of the controls on the back--there is a small chance the pots may be corroded. If the amp is dead the best bet may be to replace the plate amp (see Parts Express or ApexJr for example) or just buy a new sub.