Senerateles Does your computer have multiple drives, and have you tried installing the game onto a different drive? Is the drive you've been using internal or external? And if you use a third-party antivirus, did you in fact disable it while creating the new folder and trying to install the game? I realize this might not sound like the safest practice, but as long as you're not doing anything else, your computer should be fine.
Please also let me know exactly what happens when you're trying to install Medieval, including a screenshot of any error message you get. There are a number of download issues that look similar but are not the same.