The best way to install is with a clean install. I beleive you click on Custom after booting from the DVD or flash drive you have 8.1 on. Then delete all previous partitions that had Windows, EFI, etc. just leave the partition you had personal files on and then install 8.1 to the unallocated space. Use the generic key to install 8.1. Once inside 8.1 right-click on Computer . Properties and then click on something like Change Product Key and enter your Windows 8 Pro key. Then if you had Windows Media Center, type Add Features in the Search box, click on already have a key and enter it. After it's installed and your pc restarts, run Windows Update and install all updates. Do that a few times until none are found. Then proceed with updating/installing drivers and then your software. Also search the Store for app updates, too.