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:

C:\Users\<Username>\AppData\Roaming\Adobe\Lightroom\Preferences

2. Disconnect all USB Controllers. Lightroom disliked my connected Windows 8 Phone so go check those devices as well.