Occasionally, you may encounter unexpected restarts of your Windows VPS. 

The source of such restarts may vary and can be caused by several sources such as and not limited to: 

• Windows Automatic / Manual Updates
• Application Related Restarts (intempestive / scheduled) 
• Resources Outages 
• Windows Related Errors 

Though-out this guide you'll see how to troubleshoot the situation and assess the exact cause. 

To proceed, you would need to open the event viewer as indicated in the screenshot below: 

Once opened, you'll be able to isolate the critical events which includes all server's unexpected restarts:

You may then isolate the kernel-power or review the logs which lead to the Windows server outage.

That's it! From these logs, you'll be able to accurately determine the source of your situation for your Windows dedicated server or Windows VPS.