The likelihood is that now you have successfully sealed your map, VVIS is running properly, and that can be a very time-consuming process. So much so in fact that it will cause Windows to think that your compile has frozen. It hasn't, it's just doing a lot of work in the background.
You could:
1. Get Hammer++, which has a replacement compile window that does not freeze, or
2. Use the batch compile tool CompilePal. This is a separate GUI for compiling maps, which comes with several extremely valuable tools. I strongly recommend it.