Hi
Presumably you are going through the "Save Movie" option and entering the required values. Following this there is a "Converting Video" window. At this point little appears to be happening particularly if your video is a long one. It may take minutes (sometimes many minutes) before the blue task progress line starts to arrive or the video position starts to register. If this is the case then you may well think your PC has frozen.
If the program has crashed then you might try reloading it again from scratch.
You could also check the video creation process with a test video of a very short clip, say of just a few seconds length.
Nat