Of course, and you should! Not only is recycling old computers good for the earth, it also keeps dangerous materials like lead, mercury, and cadmium out of landfills.
Reusing old computers can be done in a number of ways. You can drop off your old electronics at many city's electronic recycling programmes so they can be thrown away properly or fixed up. You can also give your old computers to charities or non-profits that fix them up and use them for learning or helping people in need.
For your own safety, make sure to erase your hard drive before you recycle it. To make sure your information stays safe, you can use special tools or get help from professionals.
Don't let your old computers sit in the attic and get dusty. Recycle them to give them a new start!