When troubleshooting a Windows Server you can easily found out since when the server is booted by the command:

systeminfo | findstr Boot

But then you still don’t know why and by who. The following command in PowerShell helps you with this:

$EventIDs = 41,1074
Get-WinEvent -FilterHashtable @{ LogName='System'; Id=$EventIDs } | ft -AutoSize -Wrap

This give a list about when the system has rebooted. As long the System Event log has not be cleared out.