Well, Lynda, here is what I suggest.
First, try another SD card to make sure the issue is not with the card itself. If another card works, then the issue is with the card.
If it is NOT the card, you will probably need to reinstall the drivers for the SD card reader. You can get to this in Windows by pressing your Windows key (in between CTRL and ALT on the left side of your keyboard) and the letter R at the same time. A search box will come up. type in devmgmt.msc and your device manager will come up.
The device you are looking for will be under IDE ATA/ATAPI controllers or memory technology devices and will be labeled as a card reader.
Right click on the device once you find it and click uninstall. Do NOT click the check box that will delete the driver information.
Then, at the top, click ACTION and Scan for hardware changes.
This should reinstall it.
Once reinstalled, try the card again and it should work.
If this doesn't work, reply so we can try something else.
If it DOES work, remember to rate my answer so that I may receive credit and continue assisting other people!