My license just closed

Hi!
I have just downloaded unity3d on my windows 8 computer but I have a problem with my license. It says that it is an error and that Unity will close.
How can I fix this?

Have you attempted to uninstall and reinstall Unity? If that fails, it sounds like your license is the issue in which case I would contact Unity directly using this form:

http://unity3d.com/company/sales?type=sales