Why is my camera not recognizing SDHC card?

Yesterday I took pictures and loaded all new pictures from the SDHC card to my computer (via the camera with a cable to my computer). I then ejected the card and put it into my camera. Today when I tried to take pictures it said No Card. The card was inserted properly and unlocked. I tried a different card and got the same thing No Card. The cards do have pictures on them that are visible and accessible via my computer. The battery is half charged.