Many thanks to you all for this advice, which I will certainly take.

Help if possible, please.
My K5 -2years old- has started to refuse to upload all the shots taken via usb to the computer. This seems to be an incremental issue with the maximum number of uploads falling off in the last three shoots. There seem to be no other problems with the camera of which I am aware.

Any ideas, advice, guidance would be most welcome.

The additional information that has arrived since my original post is most useful. Thanks to all.

Thank you for this. Useful info, if a trifle condescending in places. But, I am grateful for the genuine help.

Pentax user from 1972 also Bronica.

It must be me! I can enlarge the shot in camera and select a particular area. What I cannot find a way of doing ( and two letters to Pentax having been unanswered,) is find a way of capturing the enlarged area to download to computer. It was so easy with Sony. I did read the instruction book; so, it must be me. Help from anyone, please.