OEM or Original Equipment Manufacturer licenses are typically tied to a specific motherboard. Retail Licenses can be installed to any PC, as long as it is installed to only one PC at a time.
buying OEM usually means replacing the OS with a new copy when you upgrade the system. New motherboard will demand a new license.
Retail can go from your first computer to your third computer as long as it only installed to one PC at a time. new motherboard no problem, license wise.