Here are some things to try if your computer either won't turn off or turn on.

[+Warwagon MVC]

Here are some things to try if your computer either won't turn off or turn on.

If your desktop / laptop is frozen and refuses to turn off. Hold the power button on either the desktop or the laptop in for 10 seconds. That will force the machine to turn off.

If your desktop refuses to either power on or give you any display on the screen, simply unplug the power cord from the back of the desktop. Then press the power button 3 or 4 times. Then plug the power back into the desktop and try turning it on again.

If your laptop refuses to power on do one of the following depending if you have a removable or non removable battery.

Removable battery

Unplug the AC adapter from the laptop and take the battery out. With both of this things disconnected, press the power button on the laptop 3 or 4 times. Then reconnect everything and try turning the laptop on again.

Non removable battery

Unplug the AC adapter from the laptop and flip the laptop over. On the back of the laptop look for a small pin hole you can push and hold for 10 seconds using a paper clip. After doing that, plug the AC back in and try turning the laptop on again.

[Anibal P]

For the HP laptops at work was make them remove the battery and hold the power button down for a minute instead of pressing the button repeatedly 

[JJ_]

When my PSU was on its last legs at the turn of the year I read in its manual that turning the PC off at the mains and keeping the case power button pressed for 10 seconds discharges any power stored in the capacitors. I tried this and my PC eventually tuned on. That was its problem, it would randomly fail to power on a cold boot. RMA'd the faulty PSU to XFX and got a Corsair as a replacement. It's been plain sailing since

[Ian S.]

If my Surface doesn't wake, I disconnect everything including the Keyboard, then press and hold power for 15 seconds,

[Tidosho]

The short circuit protection in most modern PSU's will trip a relay if an electrical fault occurs inside your computer, this will give the symptom that it will not power up. The relay will NOT reset until the mains is unplugged, and plugged in again. Obviously you'll need to find out what caused it to trip, otherwise it will just trip again when you power up with a big click.

 

I see it a lot with hard drives when the TVS (Transient Voltage Supressor, in layman's terms, overvoltage protection!) diode or a DC-DC regulator is shorted, a TVS either blows open and stops the hard drive powering, or stays shorted if faulty, tripping the PSU short circuit protect relay. If the TVS gets over 4,000v which is its maximum, due to a cheap PSU with awful surge protection, it blows open and normally takes other stuff out with it on the HDD PCB, which causes permanent shorts.