Computer powers on and then immediately turns off
If your computer turns off immediately or even within a few seconds after it is turned on, there could be several possible issues. To proceed, we suggest going through each of the following sections in order as they're meant as a step-by-step guide to help find a solution to your problem.
Note: See our no power or computer does not turn on document if the computer is not coming on at all. If the computer has been on for several minutes before it turns off, see our computer turns off without warning document.
Caution: Some of the steps below require you open your computer. While working within your machine, always be aware of the dangers of ESD.
If the problem persists, make sure all cables inside the computer case are firmly attached to the motherboard and each component. You'll want to check the IDE cables and SATA cables, which are typically connected to the hard drive, CD or DVD drive, and floppy drive (if present). Check both ends of each cable and make sure they are firmly attached to the component and the motherboard. Turn on the computer and test to see if this resolves the issue.
Tip: Sometimes the best way to verify a cable is not loose is to disconnect and then reconnect the cable on both ends.
An electrical short in a computer, which may cause power issues, happens when pieces of metal cause a path for electricity to flow through that shouldn't exist. Computers are full of screws, as they hold nearly ever internal component in place, and from time to time they can come loose. Lift up your computer and gently rotate it while softly shaking it from side to side. If you here what sounds like small rocks banging around, it's likely that you have loose screws inside the case. Open the computer up and remove them.
Verify the memory modules are properly seated in the memory slots on the motherboard. To do this, open the computer, remove the memory modules from their slots, and gently reseat them. It also is important to note that memory modules should be installed in pairs and in matching slots, which are designated by matching colors. Make sure the chips are firmly seated and the clamps on both sides of each chip snap into place. Plug in the power cord and turn the computer on to see if the issue is resolved.
Power supply issues
Power supply voltage switch
In some cases, a power supply voltage switch, which is the small red switch located the back near the one for power, can be on the wrong setting. If this switch's setting is not correct for your country, your computer may not stay on. The first thing to do is consult the Voltage Valet website to discern your country's correct settings. After you know them, make sure your power supply voltage switch is set accordingly.
Possibly defective power supply
The next thing to check is whether or not the power supply is functional. A faulty power supply can result in not enough, if any, power getting to the motherboard, which would cause the computer to shut off immediately or not turn on at all. Many online computer retailers sell power supply testing units that may be purchased for under $20. In the event of a bad power supply, the only remedy is to replace it with a new one. Fixing a power supply is not an economical solution, if it's even possible at all.
If this is a new computer or the motherboard has been recently replaced, make sure that the thermal compound is properly applied to the processor. If the heat is not being properly transferred from the CPU to the heat sink, it can overheat almost immediately.
The last thing to check would be the motherboard; however, this can be rather difficult since the issue could be just about anywhere in the circuitry. A faulty circuit or malfunctioning component (e.g., capacitor) can cause the computer to shut off immediately or not turn on at all. If none of the above recommendations help resolve the issue, we suggest sending the computer to a repair shop or replacing the motherboard.