Troubleshoot POST Problems

Every PC goes through POST--power-on self test--when it first powers up. One mistake many new system builders make is to assemble the entire system, then try the first boot. The problem with this approach is that it's difficult to narrow down the actual culprit behind a boot problem. Instead, install the CPU with CPU cooling solution, memory, and the graphics card. Don't connect hard drives, external storage, or optical drives. Don't install additional expansion cards yet, either. Try a bare-bones boot first, with only the monitor and keyboard attached to the system.

With that in mind, let's look at first-boot issues.

Nothing happens on startup. After attaching the monitor and keyboard, you press the power switch and... nothing. The fans don't spin up, lights don't come on. The system appears to be completely DOA. While it's possible that the motherboard is completely dead, it's been my experience that defective motherboards will still light up their diagnostic LEDs. If you're getting no indication of power, something else is likely the culprit.

* Is it plugged in? This may seem like a ridiculous thought, but it's worth checking the power. Even if the power cord is plugged in, I've found that the plug to the system PSU might not be firmly seated. I've also plugged systems into power strips, but the strip itself wasn't turned on or plugged in.

* Check the switch on the power supply to make sure it's in the "on" position.

* Check the internal power connections. Ensure that the main power and the ATX12V connector (a small 4- or 8-pin connector) are both firmly attached.

* Check the power switch and reset switch connectors. I've sometimes reversed these, and discovered I've made the reset button the actual power button by accident.

* Check under the motherboard--you might have a grounding problem. I once found a motherboard mounting nut installed in the wrong location inside the case. It was in exactly the right place to create a ground fault in contact with the back of the board. After removing the nut, the system booted without a hitch.

* If possible, try another power supply. A dead power supply can certainly prevent a system from powering up.