I tested the unit with Windows 10 provided, and it worked fine.  I installed extra hard drive, replaced the power supply with twice the total output and then installed Linux Mint 19.1.Lets just agree that Windows 10 does not play nice with Linux.  And Linux Mint is no exception.  So I had a very hard time getting Arduino to work properly.  I also could not get the HDML cables to make connection. It looked like the mounting bracket was warped.I am no expert, but I can do what I need with Linux and every time I start a new project like this one I learn more.  So I installed Linux Mint 19.1 over the entire hard drive.  It took a couple of days but I am up and running happy.  Good and Fast machine.One flaw is that the HDMI outputs did not work at all.  If fact the plate where the plugs are located appears a little warped.  But the unit works fine using with the old SVGA cable.  I will probably put a fair priced graphics card, a bigger power supply (maybe 500W) and a Blue Ray Burner in the future.Great price for a referb.  And I am back up and running.