The third gear on my car has disappeared. There is no noise. You can feel it go into gear, but as soon as you let the clutch out, it is just like it is in neutral. All of the other gears work fine.
My guess is that the third gear synchronizer ring teeth are worn or broken. Doing some research indicates this is a fairly common problem with PT Cruisers. The gear teeth could also be broken, or shift fork could be damaged. Regardless, the problem is inside the transmission. Rebuild or replacing the transmission will solve the problem. I suggest having a trained professional, like one from YourMechanic, inspect your PT Cruiser firsthand.