Typically OEM versions of Windows comes with a PC and is tied to that PC.
In the EULA is usually state that you are only allowed to run that copy of Windows on that specific PC.
So not to get in any legal trouble, read the EULA that came with the PC to make sure what you are allowed todo an not.
It usually ends up with needing to buy a separate copy of Windows that is not tied to the hardware.
// Linjo