Long story. No I didn't reload office, because I am using a standalone 2016 version and my office is 2010. It's the 2016 that freezes. BUT I woke up at 1 this mornring thinking about testing it on my laptop. The stand alone version wasn't tested because it can only be on one computer. But I bought the new office package last evening which allows 5 computers (crazy system MS have). I got up, loaded office on to the laptop and tested powerpoint. Worked like a charm, and still doesn't on the desktop. So, I decided to reload the Op System Win 10 on the desktop. I set it and went back to bed.

This morning everything appears to be OK, so up I brought Powerpoint, stand alone version first. No freeze, works great. Then the new office version, and it too works fine. So whatever the problem it appears to have been an OP system issue causing powerpoint to react badly.

Problem solved, I hope forever. Thank you for the response.