First you want to make sure that the subout on your system is working. Sometimes the subwoofer is turned off or the level turned down in the speaker set up menu of the receiver.
You can connect another source(phone) to the subwoofer to check that too.
Either the woofer or the amp is bad. You can remove the woofer and try playing it with another amp or connect a different speaker to the sub amp. Usually it's the amp that goes and that is usually not worth repairing in inexpensive subs.