I was having this same problem as the OP about a year ago and found a thread with a solution that worked for me and many others but does not seem to work for everyone but it is simple and worth a try.
Take off the battery cover and place a piece of tape on the back cover where a pin from the main case next to the battery touches and battery cover.
Pics below show the are i am talking about and if you look at the back cover carefully you can see the tape over the scratch on the back cover caused by the gold pin in the other picture next to the battery release tab.
