Move command (Shift + MMB) not working

All of a sudden I am unable to use the move command (shift + MMB). Does anyone know how to fix this or has anyone else had this problem?

Works fine here. If you’re using a laptop, go to User Preferences (Ctrl+Alt+U) -> Input and enable ‘Emulate 3 button mouse’

I tried to enable the emulate 3 button mouse but that did not solve the problem. I am able to open a new 3d view window through the user preferences menu and the move command works fine.
thanks for trying.