Verified answer

Run a malware check. use free, update, do full scan. http://www.malwarebytes.org/mbam.php

Then restart, and try again.

it could take a few attempts to download, get space back on the hard drive do this, go to more options at disk cleanup and cleanup system restore points, here you will get gigs back and don't worry because the newest restore point is saved, this process takes time, wait till the ok button becomes active again

also don't use a wireless network when downloading, plug in the ethernet cable