Hi,
Do you connect other monitors?
If yes, please change the mode to Duplicate for a test.
When there is only one monitor, in PowerPoint, please go to Slide Show > Monitor, select Primary Monitor and then close PowerPoint. Then right click the desktop > Display settings > Make sure this monitor is the main monitor. Restart PowerPoint to have a check.
Besides, I find a similar thread you may have a look, "PowerPoint won't get into presentation mode", it is about settings of Nvidia graphics card.
Any questions, please let me know.