After importing a file, Lightroom stops working. This might not be a solution for everyone but here are two things you can try:
1. Delete the Preference file located at
“%appdata%\Adobe\Lightroom\Preferences” (just enter this at Start->Run or WindowsKey+R)
or the long way:
2. Disconnect all USB Controllers. Lightroom disliked my connected Windows 8 Phone so go check those devices as well.