Sometimes your computer may appear to be unresponsive when you turn it on, you briefly saw life on the screen and then it went blank and has been like this for a little while. It could be the case that Windows is installing updates or the disk is being checked - you can check for activity of the hard disk by observing if there are any lights flickering on your computer or you may be able to hear the hard disk working away. You could simply wait for 5 to 10 minutes.
If your machine has been in this state for some time, perhaps longer than 10 minutes you can perform what is known as a hard reset - press and hold the power button for 10 seconds or so - this will force the machine to turn off regardless of what it is doing. Then try powering back on. If you keep encountering the issue, raise a support ticket by e-mailing email@example.com to arrange to have your machine looked at.