SOLVED My card reader for sending photographs to my computer has stoped runing.

[Trouble]

The new hama works perfectly with the same CF card from the same Canon EOS 300D yet I assumed that the Windows 10 computer had refused to work with my elderly Canon EOS 300D

The fact that you are removing the memory card from the camera and inserting it into a card reader, pretty much takes the camera out of the equation.
Under those circumstances it really doesn't make any difference if your camera itself is compatible with windows 10 or not.

I was looking forward to your results from attempting to interface the actual camera (with memory card in place) with your computer as suggested by canon in your post #13 above