If your file is corrupt, try re-downloading it, possibly in incognito mode or with a different browser to make sure you're not using the cache. If you're having trouble unzipping it, you may need to use a program like 7zip or WinRAR.
I don't have any other solutions, sorry. If it's not working for you on multiple websites and through multiple browsers, then it might be a problem with your firewall or internet connection, and I cannot help with that.
