Before you go the software route here are a couple things to try.
A few times I have pulled the card from my canon DSLR before the camera was shut off and the card would not read on the computer. I put the card back in the camera and turn it on, then off. Then I turn on the camera and take a picture and shut off the camera and remove the card and the computer would read the card fine. I don't know why, it just worked!
In another instance I had to wire the camera directly to the computer with the supplied cable, with the card in the camera, to see the files on the card.
Good luck.
T2i, 17-55, 24-105L, 70-200ISF4L, 400 f5.6L & a bunch of old MF lenses.