Automatic reboots can be caused by several different things and are hard to diagnose. One thing you can try is turn off the automatic reboot option under the recovery options for your computer. This will make it so your computer won’t reboot on errors so you can see any problems. Go to to System in Control Panel and go to Advanced System Settings. Then click on the Advanced tab and then the Startup and Recovery Settings button and uncheck the box that says Automatically restart. The next time you reboot, it should stop on the Blue Screen so you can read what it says.
The next thing to look at is to see if you have installed any new software or drivers or even any new hardware on your system. Faulty drivers can cause reboots as well. If so you may want to uninstall the software or remove the new hardware and see what happens.
There can possibly be a problem with your motherboard's< a href="/support-categories/hardware/487-what-is-the-bios" target="blank">BIOS. You may want to do a BIOS update if there is one available. Just be really careful to do it correctly because you can ruin your motherboard if you don't.