Here are a couple of simple things to keep in mind about your computer, to help it have a good long life.
Your PC should always be plugged into a power strip/surge protector. Power spikes and outages can cause major hardware and software issues. If you experience frequent power outages, you may want to consider getting a battery backup surge protector.
Make sure there is sufficient air flow around and through your PC. Don’t run it inside a cabinet with the door closed. Overheating can cause parts to wear much faster, and can lead to irreparable damage.
Use a can of compressed air to blow out the vents and fans on a regular schedule, like monthly or at least quarterly. Unplug the power from the PC and take the cover off. Blow out the inside of the system, and put it back together. Once you’ve done it a time or two, you’ll see how easy it really is.
Don’t have liquids around the system. Spills can cause major damage, in a flash.
All in all, just use common sense and you can keep your system running a whole lot longer.