The problem: inserting my memory card into the card readers on the front of my HP Pavilion did not bring up the Auto-Play option. Furthermore, after opening Windows Explorer the drives were no longer listed. Several of the posts I had found mentioned restarting the machine, some mentioned "uninstalling" all the USB devices in the Device Manager, but the one key item that I still could not find the original source was the "hold down the power switch for 4 seconds after shutdown". I have no idea what that does, but it seems to me to act like "cache" flush and Presto!! My drives magically appeared again.
Well,
HP forum note that I thought I had found the answer earlier on.