You've finally gone and bought a new PC. It has a boatload of memory, lots of cores, and a fast, modern graphics card. But now your old computer sits in a corner, and although you know it's just a machine, it seems to be sulking like a puppy that missed its morning biscuit. It's weird, but you feel guilty with the whole idea of throwing it out.After all, it's perfectly functional. When you first bought it, it was near state-of-the-art. If your new PC replaces one that's really on its last legs, by all means, take it to a reputable electronics recycler. But it's amazing how many users ditch perfectly good machines when they pick up a shiny new system.You can do plenty of things with an old PC besides sending it to the recycling heap. Let's take a look at a few ways you might put that old system to work.