Now, the moment of truth -- it's time to turn your machine on and see if it works. If there's a switch on the back of the power supply, make sure it is on. Also make sure that the power supply is set correctly to 110 or 220 volts (some power supplies do this automatically, others have a switch or a slider).

Then push the power switch on the front of the case. In the ideal case, four things will happen:

You will see/hear the fans spin up
You will hear the hard disk spin up.
Lights will light on the case.
You will see something happening on the monitor to indicate that the motherboard is alive.

If you see/hear all of that happening, you are successful. You have created a working machine. Using the manual that came with the motherboard you can enter the BIOS screens and make sure everything looks OK. Chances are you will need to set the machine's date/time, but that is probably all you have to do. Everything else is probably automatic. All the drives will be recognized and auto-configured. The default settings on the motherboard will be fine.

The next step is to install the operating system. And presto, you have a working machine of your own creation. Congratulations!

Troubleshooting
What if you put it all together and it doesn't work? This is the one possible downside of building your own machine. It is hard to describe the feeling you get when you try turning on the machine and nothing happens. You have put in several hours of work and a significant amount of cash, so it's discouraging to get no response.

All is not lost, however. Here are several items to check:

Is the power supply firmly plugged in and turned on (many power supplies have a small switch on the back)? Try a different outlet.
Did you plug the power supply into the motherboard? Look at the manual for details.

Make sure that your motherboard is connected to the
power supply.
Is the case's power switch properly connected to the motherboard? If you have plugged the switch into the wrong pins on the motherboard, it will not work. Check the motherboard manual.
Are the drives connected to the motherboard properly? Do they have power?
Unseat and reseat the video card. If the motherboard has onboard video, try to remove the video card completely and boot using the onboard version.

If you have checked all of that and nothing continues to happen, it could mean:

The power supply is bad
The switch on the case doesn't work. We actually had this happen once on a machine we built at HowStuffWorks.
Something is wrong with the motherboard or the CPU.

The easiest way to determine where the problem lies is to swap parts. Try a different power supply. Swap a different motherboard into the case. Play around with different combinations.

If it is still not working, then you have a few options at this point. You can go back to the shop that sold you the parts. If you bought them from a small local shop, they can help you debug the problem (although it may cost you). If they sold you a bad motherboard (rare, but possible) they will usually help you out. You can also try to find a more experienced builder who would be willing to help you. There is a rational cause for the problem you are experiencing -- either a bad part or a bad connection somewhere -- and you will find it.

Now that you've seen how simple it is to build your own computer, we hope that you'll give it a shot. You'll have a computer that you understand completely and will be easy to upgrade. You can save money, and it's a lot of fun too. So the next time you need a new computer, consider building it yourself!

For lots more information about computer parts, check out the links on the next page.