Will try-thanks so much!

My boys have a Desert Forces train that is about 2 years old. It has always run well(they do not leave it out all the time).  Recently, the train pauses as it runs, especially at the straight track parts (it is shaped in an oval-7 curved then one straight-then 7 curved-then one straight-16 in all). One car in particular will cause the entire train to stop running-although the rest work well. What can I do to fix it? Is there something connected wrong? I spent an hour staring at each tiny piece to see that the EZ track is connected properly and I believe it is (those little gold connecters get shifted). I'm guessing that there is two problems-one is the obvious not working car and another is something else and I'd like to fix both problems. I know nothing about trains and am stumped at what to do next. Can anyone help?
Thanks!