try verifying in game files and defragging them. You do this by right clicking on INS in your Games tab and selecting properties and i then local files. If that fails. Reinstall INS.
Sounds like it already tried to download, but for whatever reason did not finish or was corrupted. I would suggest the reinstall the clear the folder and try the download again. But I'm also not a super-techie-genius anymore. I still like my Windows 98 format...