Laptop not turning on: checks from the power adapter to a power reset

Unplug the adapter or the plug from the wall socket before checking anything. Make sure your hands and the work surface are dry.

Unplug the charger and switch the device off. Never puncture, bend or heat a swollen battery.

Inspect the adapter and its cable while they are unplugged from the outlet, and do not use an adapter that smells burnt.

The first step is to pin down which problem you have, because the fixes differ. Press the power button, then watch the indicator lights, listen for the fan and look at the keyboard lights.

HP writes that a spinning fan or sounds from the laptop mean it is actually on, and the problem is the display, not power.

1. Use the adapter and cable that came with the laptop or an official replacement. ASUS asks you not to mix adapters between products because their power output specifications can differ, and HP writes that an adapter with the wrong voltage can damage the battery.
2. Check the three connection points ASUS names: the cord into the adapter brick, the plug in the outlet, and the plug in the laptop. All three should sit firmly without wobbling.
3. Look at the light on the adapter brick if it has one. According to HP, that light shows power is reaching the adapter from the outlet; if it is off, try another outlet.
4. Plug the adapter straight into a wall outlet. HP writes that power strips and surge protectors can fail too, so do not test it through a multi-outlet adapter.
5. Test the outlet with another appliance, make sure it is not controlled by a wall switch, and check whether the MCB (the circuit breaker) in your home has tripped.
6. Run your fingers along the cable while it is unplugged. Look for cuts, sharp kinks or exposed wire.

If the adapter brick is discolored or warped, smells burnt, or there is melted plastic at the plug, stop using it. HP and ASUS both say to replace a damaged adapter through authorized service.

A battery that has run completely flat needs time before the laptop will start. HP suggests leaving the adapter connected for 15 to 30 minutes even if no light comes on, then trying to turn the laptop on with the adapter still connected. ASUS suggests leaving a laptop that has not been charged for a while to charge overnight.

If the laptop starts with the adapter but dies as soon as the adapter is unplugged, the battery is weak or has failed. A laptop with a removable battery can be tested the HP way: remove the battery, check its metal contacts, then start the laptop on the adapter alone. If the laptop starts without the battery, that battery probably needs replacing.

Most laptops today use a built-in battery that is not designed to be removed by the user. For these laptops, HP describes a battery reset that does not involve opening the case; it is in the next section.

A hard reset drains the leftover electrical charge and temporary configurations that can stop a laptop from starting. The method differs between brands, so follow the instructions for your laptop's brand.

The HP method: turn the laptop off, unplug the adapter, remove the battery if it is removable, then press and hold the power button for 15 seconds. After that, reconnect the adapter and try to turn the laptop on. For a built-in battery, HP suggests holding the power button for 15 seconds with the adapter unplugged, then charging for at least 30 minutes.

The ASUS method, called an EC reset and RTC reset: remove all external devices, turn the laptop off, connect the adapter, then press and hold the power button for 40 seconds. Some ASUS models use a 20-second press instead; on those models the power light flashes quickly after about 15 seconds, and you release the button once the flashing stops.

Before any reset, disconnect all external devices such as external hard drives, printers, memory cards and dongles. ASUS says these devices can interfere with startup.

If the fan spins and the power light is on but the screen stays black, try raising the brightness with the function keys. The brightness may be turned all the way down; HP names Fn with F2 or F3 as the usual key combination.

Then connect an external monitor over HDMI or VGA. According to HP, if the external monitor shows a picture, the laptop screen or its display cable has failed. If the external monitor stays dark too, the problem may be in the graphics card or the motherboard.

A laptop that reaches its startup screen can be checked with the brand's built-in diagnostic tool. HP provides HP PC Hardware Diagnostics, which opens when you press F2 repeatedly right after pressing the power button. ASUS provides a battery check in the MyASUS app, and you reach the BIOS screen by holding F2 while pressing the power button.

A laptop that starts again after a reset still needs checking so the problem does not come back. ASUS and HP suggest three things.

• Test the adapter and the battery with the built-in diagnostic tool. On an HP laptop, open HP PC Hardware Diagnostics from Windows, then run the AC adapter test and the battery test. On an ASUS laptop, open MyASUS, select System Diagnosis, then Battery problems and Checkup with the adapter connected.
• Update the BIOS, Windows and drivers. ASUS says these updates improve system stability, battery charging problems included.
• If the battery will not charge, ASUS suggests reinstalling the battery drivers through Device Manager. Uninstall Microsoft ACPI-Compliant Control Method Battery and Microsoft AC Adapter under Batteries, then restart the laptop so the drivers install again automatically.

Write down any failed test result. HP asks you to note the failure details or codes, because that information helps support find the faulty component faster. If every test passes but the laptop still sometimes refuses to start, also note when it happens, for example after sleep mode or after the battery ran flat.

Stop checking it yourself and take the laptop to the authorized service center for its brand if:

• you smell burning, see melted plastic, or the laptop has had liquid on it;
• the adapter plug is loose in the laptop's port, which HP says usually means port damage that needs repair;
• the laptop still has no power after you try another suitable adapter, charge it for half an hour and do a hard reset;
• the bottom case or the touchpad looks raised, which can point to a swollen battery;
• the built-in diagnostic tool reports a failed battery or adapter.

Work that needs the case opened, such as reseating the RAM, replacing a built-in battery or repairing the power port, is a job for a service center technician. A laptop holds a lithium battery inside its case; opening the battery pack or replacing the battery cells is not something to do at home. Tell the service center which steps you have already tried, and if the laptop still starts for a while, back up your data first.