Marilyn, Another thought. I don't recall if you ever said that your writer will write and read ordinary files, like a hard drive.
If your device is working, you should see it listed as a disk drive when you open Windows Explorer (only if there is an SD card in the reader). If it is there, try dragging any file from your hard drive to the Sandisk drive to see if will copy to the SD card. If so, you should then be able to drag that file from the SD card to any other place on your hard drive. If all this works then the problem is not with the Sandisk reader but probably with compatibility. You can always delete any files that you have copied during the experiment.
Walt