Also, it could be a bad neutral. In which case the hot still has a potential of shocking you when you are working on it. The two tools I find indispensable for this kind of situation are a non-contact tester and a plug tester. Which would cost around $30 probably if you buy the cheaper ones, they work just as well for a handyman who uses them rarely. Here are a couple of links to what they look like.
http://www.homedepot.ca/product/non-...-tester/918753
http://www.homedepot.ca/product/outl...-1-clam/963591
The nice thing about the plug tester is it tells you what the problem is, giving you a place to start from!