Did you edit this post when I wasn't looking?
I ran chkdsk through cmd, but this was before catching the 'run as admin' bit, and it said the drive was locked as it was ntfs, and something about doing the scan on a restart. So I did that. It ran through and recovered a bunch of orphaned files this time, restarted again, I tried to run the installer, and...
It's working perfectly now. Thanks a lot for your help guys. Really quick and to the point!