Hi Yekar Yangdon,
Could you give us some more details about the problem? Are you sure the laptop is actually turning on when you press the power button? Do you hear all the typical sounds and beeps?
I would start by testing the laptop with another screen. Use a monitor or a TV. Any changes?
If not, it is likely that the problem is PC related and you should seek help from a technician. If the PC is under warranty, call the seller.
One thing you can try: remove the battery and disconnect the power cable. Hold the power button for 30 seconds and then reconnect the cable. Try to boot again.
Hope this helps