The problem then becomes: What should you do with your old machine?
Leaving it sitting in the corner isn't exactly a good long-term solution. Eventually, you'll have to part with it in one way or another, and just as there are stages of grief, there are stages (or steps, if you prefer) that you'll have to go through as you get rid of your old, trusty bucket of bolts. And each one requires some action and thinking on your part.
Stage one: Look for a secondary use
Before you ditch your rig, consider your options. If you've got a lot of digitized media, it could serve as the hub for your home media server. Just hook it up to your home entertainment center and — poof! — you've got an easy way to access videos, pictures and music streaming sites from your couch. Other options include turning it into a backup storage device or a home security monitoring system.
Stage two: Wipe it clean
If you can't find another use for your PC and are determined to get it out of the house, you'll want to be sure that any and all personal data is nuked. Once you've verified that you have a backup copy of everything critical, it's time to make sure that data doesn't fall into the wrong hands.
While many people think simply reformatting the hard drive is enough, there are a few extra steps to take to ensure no one can access your files. Encrypt your sensitive files through either a specialized program or using the built-in Windows encryption system. Once they're deleted, they can't be decrypted -- even if someone manages to recover them later. Another option is using a dedicated drive-erasing tool, like DBAN, which overwrites each block on your hard drive several times.
Stage three: Consider philanthropy
Once you've erased your digital fingerprints, you have a few ways to go. There might be profit potential in the machine, but before you decide to cash in, think about others who might need a new PC.
Whether it's family members whose computing needs aren't as demanding as yours or a local school that doesn't have the budget to buy new equipment, there are plenty of people and places that can likely use your old system. You'll also get the bonus warm fuzzy feelings that come with helping someone out -- and maybe a nice tax deduction as well.
Stage four: Profit
Need to finance your new purchase? Assuming your old system isn't antiquated, there could be gold in them thar circuits. There's always a market for used computers, so take to eBay and Craigslist and try to track down the going rate for comparable systems.
Be warned, however: what you think a machine is worth may not be realistic in the free market. Also, the usual safety rules apply when making any sort of online purchase.
If you can't find a buyer for the system as a whole, take a look at the parts. You may have a mid-range system with a top-of-the-line graphics card or premium RAM. If so, you have the option of recycling this hardware in your new system or finding a buyer for it. Again, eBay and CraigsList are good options, but if you're a regular poster on a gaming forum, you might find an enthusiast looking to upgrade their machine. And those people are more likely to offer a fair price.
Stage five: Trash it
Eventually, you have to let the dead go. That Pentium 4 served you long and hard, but its glory days are long behind it.
When there's no new home waiting for your PC and the parts aren't up to modern standards, the trash heap is all that remains. Instead of putting it on the curb, though, do the environmentally-responsible thing and find a local recycling center. If you don't have one nearby, most electronic retailers like Best Buy and Staples offer consumer electronics recycling. Last year alone, Staples collected more than 10 million pounds of old technology to be recycled.