'Waiting for input'

I've seen several posts on this particular matter, but none seemed to contain an exact answer! My fruity loops was working fine all day, then as soon as my mate arrived and I tried to play him a new idea, i only get 'waiting for input' and the play logo turns to ... not even a pause sign?!?!?? Please help, I've only recently got the programme and can't work out what's going down! Cheers.