There are many reasons why a computer won't turn on, but a complete loss of power is not the worst-case scenario. There is a chance that your computer isn't receiving power because of a serious issue, but it's unlikely. In most cases the Power Supply Unit (PSU) requires repairing or replacing.
Faulty power supply units can cause desktops, laptops & tablet computers not to power on. Even if it appears that your computer is receiving power, lights are on, fans are running or even if it powers on for just a moment this can be caused by a faulty PSU.