W7Pro64. Run BIOS in legacy mode. Update to the latest BIOS (3.91). Quality RAM all identical sticks, all 8 slots filled, assuming you're running 1 processor, which you are.
Make sure you have latest firmware from Samsung.... some earlier firmware from them has been stink.
Clean install.... know how to get the small system reserved partition on the install.
That is an excellent workstation.... do not despair.