Why is it not powering on

This may be a hardware problem, but to find out which specific part is at fault will require some troubleshooting. iFixit has an article that may help you: ASUS Q400A-BHI7N03 Troubleshooting

@james37247 you are not giving us much to work with here. It would have been nice to know what you have already checked and what you have already tried.

Anyhow, You gotta start somewhere, so might as well start off Start off with the easy things. Disconnect the power from the computer by unplugging the power cord from your computer. Disconnect all external devices from the computer. Now hold the power button depressed for about 30sec-1min. Reapply the AC power adapter and see if your computer does show any sign of life.

Next you will want to check your power supply. Make sure it has the proper voltages. Check to make sure that connectors are not bend etc. Check the DC-in jack of your laptop. Make sure there is no corrosion, debris etc. that prevents it from working. Clean it of any debris etc, use a few puffs of air to clean it out. If none of this works, get an ammeter and see if your laptop draws any amperage from the charger. After that, you need to check and see if your motherboard even gets power. For that of course, you need to open it up. Post Some good pictures of what you see. That way we can see what you see. Adding images to an existing question