Lindsay,
Guest OS type is a drop-down box at the top of the 'General' tab of the Virtual Machine configuration window. It gives Parallels a hint on which operating system is installed in the Virtual Machine. Since you run Windows 10, it is better to set it to Windows 10.
However if it fails to work somehow, you may open a command prompt with elevated privileges in Windows(step 1 at SFC Scan link above explains how to do it), input 'powercfg -h off' into it(without quotes) and hit Enter.
Last edited: Aug 19, 2015