Hi,
You are most likely experiancing what is known as a "Blue Screen of Death" (BSOD), as most of these errors are fixed by a re-boot, this is the default response in Windows. How ever if the reboot does not fix the issue, you are stuck with a computer that reboots every time it tries to start with no indication as to what the problem is.
Read the information on this link that explains how you can disable this behaviour:
http://www.eightforums.com/tutorials/4924-advanced-startup-settings-boot-windows-8-a.html
If on the following reboot you computer continues to reboot then your problem is more fundemental and you may need to consider restoring your computer to a backup image, or factory default. It may even be caused by serious hardware failure.
If you do get a bluescreen with a load of white writing, take a photo of it and post it here. The information contained is often enough to get you sorted.