Hi Ralph
I am Dave, an Independent Advisor, I will help you with this . . .
The actions associated with the function keys are set by the manufacturer of your PC . . .
If you press the Fn Key + F5 does that result in a refresh and also starting a PowerPoint presentation
If so, a Windows 10 update may have reversed the need for the use of the Fn key, try pressing the Fn Key + Esc to see if that toggles the need to press the Fn key
If that does not work, boot your PC into BIOS, in there you may find a setting to toggle between Media Keys and Function Keys