I would just bring it to a local computer store. They will give you some money for it, and then resell it someone else. No wasting your time trying to sell it yourself, and no need to have strange people come to your house. The problem with desktops is that they really are too expensive to ship.
I guess the 10,000 RPM on the hard disks was not an adequate speed to make the "trading computer" profitable. 10,946 RPM would probably have worked better for the OP.