If you have tested all the above, the only other thing I can put it down to is the Capsule (the bit with the diaphragm in). THat may well have "gone down". Depending on model, these are interchangable, but can sometimes be more cost effective to get a new one.
As I have said in a previous post, although the sure hard wired stuff is exceptionally good and dare i say Bomb Proof, their wireless stuff is much to be desired until you spend large ammounts of money.
I prefer to use Senheiser wireless stuff myself, nothing compares!

Good luck

It will probably need to be sent to Shure for repairs. www.shure.com/service