Two things to try. Try another browser, if you used Firefox try IE9, or chrome, or whatever. Sometimes just trying it again might work as server was busy or there was a gllitch in connection.
Did you actually reinstall your operating system? These issues often occur because your oeprating system is damaged, i.e. the Windows Installer stuff...
that's the point, i don't want to reinstall it yet.
already tried that mate.