That's a pretty open-ended question.
Discard of it responsibly, part it out, sell it to computer shop so they can part it out, turn it into a constantly rotating photo album, music server for your house?
As a musician I also have an odd slant to dedicated computers for my studio. Often, having a monitor, keyboard and nearby computer that stays connected to the studio equipment beats my general-use or work-use computers having to pull double duty. Do you know anyone that might have a need for a system that would be dedicated to one task?