I had a lot of problems on my computer files (no permission, couldn't download anything etc), so I'm trying to remove everything (did the backups) and reinstall Windows 8, but when I click ''Get started'' it says:
''Insert media Some files are missing. Your Windows installation or recovery media will provide these files.''

Now I tried to follow that : Overcome Windows 8.1 Upgrade Errors With A Legal ISO Download
but when I download the windows 8 setup from there http://windows.microsoft.com/en-us/windows-8/upgrade-product-key-only, like it says in the article, an error pops up:
''Install windows We are unable to create or save new files in the folder in which this application was downloaded. Please check the folder properties to make sure that you have security permission (I do) on the folder to write files and that the folder is not read-only.''

I'm pretty confused because I already have a CD of Windows 8 installation with the CD key, so I don't really understand what I need to do. I don't know a whole lot about computers too.