Infinity HPS500 Sub problem

Does the power light come on properly? If it does, you can try hooking a dvd player (or similar device) directly to the line-in on the amp of the subwoofer (make sure sound level is set quite low). If you get no sound, then you might take the plate amp off. After unscrewing the screws, you may need to use a screwdriver or something equivalent to gently pry up the plate amp. Some plate amps have the fuse on the actual amp rather than in a more accessible location on the back of the subwoofer.

If the fuse is good, then you need to think about repairing the amp (you would need a service manual, volt/ohm meter, soldering iron, etc if you do if yourself). You might send to a repair shop (possibly check with Inifinity) but this option can be very expensive. You could also think about purchasing another plate amp (Parts Express, OAudio, etc.) and installing it yourself. In April, I used a 500w PE BASH amp as a replacement on my 9+ year old JBL PSW D115.