A "cpu" is the processor. Doesn't matter at all what OS you use it to run.

The harddrive I think you mean used to be Windows, and you want to go back to Windows?

Your gonna have to get a copy of Windows and reinstall it. Let it do the format and partition it's way.

Or, in another article I can write how to run a VM (Virtual machine) of windows through Ubuntu.

I hope this helps. If not. Reply and I'll help you step by step