No need to buy new product if you are going to re-install / start the installation from scratch. OEM = Original Equipment Manufacturer, and it has nothing to do with System Builders because they deliver the PC/Laptop with the Windows 7 Pro/HP/Ultimate by using Universal OEM:SLP Key. You can find...
First of all there is no such thing called "MSDN Testing Key". MSDN / Technet Account itself is for evaluation purpose only. If you have MSDN / Technet account you will be able to generate 5 to 10 keys for every single products. If you can see KMS and MAK key then you must be under Volume...