If a computer reboots itself on its own, the computer might have a(n) access problem. hardware problem. internet problem. software problem.

Hardware problem

Explanation:

Hardware problem can cause the computer to reboot itself on its own automatically.

The problem could arise from any of the hardware component like the Hard Drive, RAM, Power Supply, Graphic Card or  even an external devices connected the computer but also, overheating or BIOS issue could also cause a system to reboot itself on it's own.

On the other hand, the software, access and internet all need the hardware as a platform to run on. Any problem developed in this area would require the  computer to be on to rectify the problem.

Finally, If you have experienced a reboot of your computer on it's own, it is important to back up your files.