Stand the case upright, if it is not already. Ensure that no wires are touching the CPU heat sink fan. Plug your monitor cable into the video card (VGA) port, and turn on the monitor. Plug your PS/2 (or USB) keyboard cable into the keyboard port. Plug in the power cord and switch the power supply switch to the on (|) position. Press the power button.
If everything is connected as it should be, all system fans should start spinning, you should hear a single beep, and after about 5-10 seconds, the amber light on the monitor should go green, and you will see the computer start to boot.
Depending on the manufacturer of the Motherboard, you may get a splash screen, or just a memory check. The system will then halt with an error because we have yet to install an operation system. If something has gone horribly wrong, just go straight down to the troubleshooting section. If something is on fire, go to the kitchen. You do have an extinguisher, right?
Now check the front LEDs to see if you plugged them in correctly. Power off and fix the LEDS because you didn't. Test the reset button. Assuming you have got to this point without any problems, put the side panels back on, plug in your mouse and network cables and pop your favourite operating system into the CD drive, then power the system back up again. You are done assembling the computer!