Thanks for advice guys
.NET 4.6.1 would not install in safe mode - I've had a lot of problems with Windows 10 and this is a clean install of Windows 10, apart from a lot of rubbish installed as part of the Acer bundle
But skullbonz has saved the day with filehippo - a quick search and 10 minutes later, Paint.net 4.0.5 is running happily
I'm no expert with paint packages, but Paint.net is very easy to use. Since setting up 4.0.5 this morning, I've grabbed some clipart and have printed some clockfaces and pictures to help the kids learn to tell the time. Very quick, very easy, just what I need!