This could be related to overheating. Check your computer for dust, and make sure it is in a cool and ventilated place. If this is not the issue, there might be an issue with a recently installed application or software update. Hold down the power button to make sure the device is completely turned off, give it approximately 15 seconds, and try to restart the computer.
Another issue might be low battery. If your computer is a laptop and will not power back on, plug it in to the charger and allow it to charge for a reasonable period of time. If the device will still not power back on, contact your school administrator.