If it is over 10 years old...
If it is too old to use even for spare parts, and if you want to have some fun and make sure that no one will ever be able to pull any data from the hard drive, it can be fun to take an old desktop or laptop somewhere out in the country (make sure it's legal and you or a friend or family member owns the property you're on), and set up the PC on a tree stump or on the ground and use it for target practice. I did that to an old HP pavilion that was more than 12 years old and completely worthless. Other than cleaning up the mess, it was a lot of fun.
Keep Up with TechRepublic