What do you do with your old and outdated computers?

I have 2 old computers, somewhere between 12-15 years old to be more specific. I've been thinking of selling the parts since I can't actually get the PCs to boot anymore. One has a 1300 watt PSU, but it's not modular and looks like a mechanical Portuguese Man o’ War thanks to all of the attached cables. The other has a Corsair 620 PSU, and it's not modular either. They both have DDR2 RAM memory modules. Are any of these parts worth trying to sell, or should I just recycle them?