This is an old problem. The SD card is initially recognized and photos were downloaded into the PC. The same card or another SD card is not recognized on a subsequent attempt to download photos.
Any solutions? Help! cj6285
How do you connect the SD card? Are you using a card reader or a specific SD card slot? I need to know if the card and the other card that you have tested do work on another PC? If they work, then the problem is not with them, but within the reader. If the reader connects to your PC through a USB cable, my suggestion is to try it on another port or a PC.
Check the Device manager of the PC for any USB controller conflicts and if there's need to make a driver update, try do to so.