Another thing to watch while powering on the laptop is to look at the power/hard drive/charging leds. Are they on solid? Or are some of them blinking? (hard drive led may blink randomly, but if it stays on the whole time it may indicate a problem). Also you could try to hold the power button when it's off until it turns on again and back off, then release it. If not already done, unplug all other cables such as USB devices, display cables etc.
Otherwise it may be a defect in your power brick or a component is malfunctioning.