title: Why do Ipython cells stop executing?
body: <p>I'm sure this is a very newb question, so I apologize in advance. I'm trying to use ipython notebook for a group project. The program we are building is fairly large and pulls in a large number of external datasets. Much of the time, Ipython seems to stop working. I'll try to run a cell or multiple cells and nothing will happen (except a little asterisk * will appear in the brackets [] to the left of the cell). Even if I try to just add a new cell and execute 2+2, nothing will happen. What is going on here? How do I fix this? Thanks!</p>