Ensure the new operating system is compatible with your chipset model.
Ensure the new operating system is compatible with your chipset model.
For a fresh operating system, purchase it from G2A at $25 for Windows 8.1 Pro here: http://bitly.com/1kLt9pk
I believe if you've already used the key, it won't work again, though I haven't tried before.
OEM/builders might not be able to work again, though they could still try, but a retail version should be acceptable.