bad regulator?

How long is forever? It should take ~2 weeks at 15psi to carbonate properly, assuming normal chilled temperatures.

I do recommend a new regulator at some point, as being able to use 30psi to seal the top, and quick carb is quite handy.

 

Most regulators have a 'stop nut' on the screw to keep it from going further than desired. Is it perhaps the stop nut that is stopping you? If so, just turn the nut 'outward' to allow the screw to be screwed further inward.

 

When your beer is cold, you can shake the keg even at the low(er) PSIs and you will hear the gas coming in.

I assume you are keeping your beer cold, non?

 

If you have had your keg at 15 psi for two weeks you should be close if not finished. Shake your keg back and forth a little bit and you should be fine.

 

does the beer have any carb or is it entirely flat? are you sure you have gas in the tank? and all the lines are connected correctly? do you hear gas entering when you slosh the beer around? what temp is the beer?

tap the back of the gauge while everything is hooked up. tap it pretty hard, it wont break. does the needle move around alot, a little ot none at all?

 

not sure what is going on with that, could either be something wrong with internal "gate" that regulates the pressure or could be something wrong with the actual screw...but i can give a recommendation for an awesome regulator:
http://www.homebrewstuff.com/co2-regulator-dual-gauge-heavy-duty-pro-series.html
I've owned 4 different regulators and this is by far my favorite (3 are still active).
As stated though, 15psi can get you where you want carbonation-wise for like 95% of beer styles if the keg is refrigerated...