Well first off if you have an ohm meter check the fuse to ensure it is indeed good. Sometimes they can blow where you can't see them although this in not normal.
Does the amp have a light on it that changes from red to green (Or something similar) when it receives signal.
Check the cable. If you have any other RCA cable that you can replace your sub cable with to ensure it is indeed not the cable.
Remove and re-install the power cable/un-plug and re-plug into the wall.
If all these net you no results then most likely it is the amp in the sub that could be bad.
You should try to find a reputable repair center or call Klipsch, they can give you some good idea as to the cost. They are actually quite customer service oriented. It most likely will not be as expensive to repair as buying a new sub. You could at least find out the repair cost and then make a decision.
Msarva, please understand my reasoning for this comment, but I do not think the OP was looking for others thoughts or feelings about Klipsch as much as he was requesting some assistance. Sorry you had bad luck with Klipsch in the past but your post was not truly useful in any way. For the most part Klipsch is a pretty good low cost alternative in the HTIB market as their speakers have high efficiency and can be well driven by modest systems.
Candj I hope you are able to resolve your issue with as little out of pocket as possible. If you decide to up-grade please look at Elemental Designs, Epik, and SVS just to name a few. Exceptional quality and performance for your money.
Keep us posted and good luck.