Mine has the same problem and it is not rooted. If I try the dictionary a few more times, I'll get one of the following error messages
"Sorry! Activity Reader (in application Reader) is not responding." or
"Sorry! The application Reader has stopped unexpectedly. Please try again."
Googling the top message will bring numerous results from Nook users.
I agree that it appears to be a hardware problem. Mine started just after the warrantee ended.