PNGs no longer exporting with transparent background!

Can anyone help?

I work for a group of schools so I often export graphics as PNG files so they can be used in Microsoft Office software like PowerPoint.

All of a sudden, any PNG files I'm now saving have a white background when inserted into a PowerPoint. I haven't changed any settings in Corel. 

Does anyone know how to fix this? 

Thanks

  • Better solution will be using SVG instead of PNG. You can use those in PowerPoint and scale without losing quality. Also you can modify imported SVG in PowerPoint (change it's colour etc.) by using ungroup command ( SVG is converted to PowerPoint vector paths) it's much more convenient to work this way