Hook the Motherboard to the Case

In this step, you will connect the motherboard up to the power supply and all of the various case connections.

NOTE: If you have been working on a removed motherboard mounting plate, you will need to install the plate back into the case in order to be able to make the connections below.

Connect the power to the motherboard. On an AT system, find the two large 6-wire leads from the power supply labeled P8 and P9. These two connectors will connect to the large 12-pin power connector on the motherboard, usually right behind the keyboard connector. MAKE SURE THE BLACK WIRES ARE IN THE MIDDLE, RIGHT NEXT TO EACH OTHER. This is very important, because forgetting it has fried many motherboards. You may need to play with them to get them in, due to the funny little tabs placed on one side. But, they do fit, trust me. On an ATX board, the power connector is one large 20-wire plug. It is keyed for correct installation. Just plug it in. If your motherboard provides both kinds of connectors, then choose, but I recommend ATX.
Connect the CPU fan to the power. Many CPU fans connect to one of the power supply leads. They often, then, provide a pass-through so that you have a connector free for a drive, thereby placing the CPU fan on the circuit to a particular drive. Others have a little 3-pin lead that connects to a small connector on the motherboard itself. Just plug it into the motherboard. The connector is usually labeled CPU_FAN 1, or something to that effect.
Study the case connectors on the motherboard and match them up with case connector wires. The connectors are usually a big block of pins located in the lower section of the board. Some boards label the pins, but it is best to have your manual since it can sometimes be difficult to determine which label goes to which set of pins. If you have a good case, each connector will be labeled to tell you what case feature it leads to. If this isn't the case, you may have to physically trace the wires back to see what feature it goes to. When connecting, consult the manual for pin 1's, to make sure each connector is plugged in the right way. Remember, if the particular case feature is not working later, you may only have to turn the connector around on the motherboard. The following steps will outline each wire:
Connect Turbo Switch. If your case has one. If not, you can simply roll up the wire and stuff it aside or tie it up with a garbage bag tie.
Connect the power switch - ATX form factor only. On ATX machines, the power switch is connected to the motherboard instead of the power supply itself. Consult your manual. The connector is usually labeled PWR_SW, or maybe just PWR, but you must make this connection. Doing this wrong could cause your system not to start later.
Connect the reset switch. It can be plugged in any way, just make sure you connect it to the right pins. The pins may be labeled RST or RESET, but it is best to also consult the manual.
Connect Power LED/ Keylock Switch. Many system cases put these two devices on one 5-pin plug, but if you case does not have a keylock, it will be alone. The motherboard will probably be labeled accordingly. Just plug in the plug. If your system has separate plugs for each, connect them separately.
Connect the Turbo LED. Like the turbo switch, this is a relic. You can connect it if you wish, although many boards just light it and don't really do anything with it at all. If you wish, you can skip it. Some also connect it to a different part, such as a SCSI adapter, and use it for SCSI drive activity instead.
Connect the hard drive activity LED. Some come on a 2-pin plug. Others come on a four-pin plug, sometimes only two of the pins actually doing anything. Consult your manual, or play with it until it works. It is usually labeled HDD, HDD_LED, or something like that. If this is attached wrongly, the light may either never come on later or will stay on all the time when the PC is running.
Connect the PC speaker. Most cases put this onto a 4-wire plug. Just plug it in to the 4 pins on the motherboard. Other cases put the speaker connector on two 1-wire plugs. In this case, plug them into pins 1 and 4. I never could figure out why they did that…
Double-Check your work, as always.