Antonio, if the lens is the problem, there is an easy way to find out. Spend $20-50 and buy any cheap K mount AF lens you can find quickly and nearby. It shouldn't be hard to find a K mount lens in LA. The camera will either work with the other lens or it wont. Either way, you get another lens to play with, so you still have something to practice with while your 18-135 gets repaired (if that is indeed the problem)
---------- Post added 2nd Apr 2015 at 17:06 ----------
An even better idea would be to take your camera to a camera shop which has some pentax lenses and see if the AF works. I believe this mob should serve your purposes
Lenses