Why can't I view my photos?

Okay, I have an idea but I'd like confirmation or other help. Basically I've took say over 1000 photos on my 16GB card using a Canon 600D. Usually I use a Windows OS to take all of my photos off and back up, but I took it into uni today, took more photos for a stop-motion project. I had no lead to connect it to the mac I was using, so instead I just took out the card and put it into a Nikon D5000. The first problem upon doing this; the mac never found the storage device. The photography tutor tried other cameras, still to no avail. He just told me to continue compressing my stop motion project at home. So I took it away, took more photos along the way home, but couldn't find my previous photos! Got me pretty worried. When I got home, I put my card straight into my PC, using Windows 7, and couldn't find my previous photos before the ones I took on the way home. Only it says there's 10GB free on the card, when in reality I've only used 0.5GB. My prediction is that the others can only be viewed on a mac maybe? Doesn't explain why I can't see them on the camera. Oh and I've got all my photos backed up, don't worry about that.

Added (1). Yeah I understand that I won't be able to view any photos taken by a Nikon camera through my Canon. But I never took any photos on the Nikon, I took them all on the canon previously. And Everything before the stop-motion photos I have backed up twice, all I need is everything after.

I'm sure that your uni has card readers available, use one of them

You don't understand that Nikon cameras can't see images from a Canon camera. They are stored in different sub-folders.

Are you using your file manager to view your memory card? It should show all the folders and sub-folders that are on it and by drilling down, you should find all your files.

My guess is that you are very new at the whole process of digital imagery and how to use a computer to find and copy image files from a memory card.

My first clue was that you took a shortcut and did not back up all your images before you took the card to the school and that instead of using four - 4 gb cards, you have one 16 gb card (all the better to lose more image files, said the big, bad wolf)

It seems that your photography tutor has a lot to learn as well.

In the future.

1) Always copy your image files to your computer at the end of each shoot
2) If you need to transfer image files to a new location, use a USB flash memory card or burn a CD and use it as your source
3) Always start a new project using a freshly formatted memory card, formatted in the camera you are going to use. If you need to switch cameras, whether to a different model or different brand, use another freshly formatted memory card, formatted on the camera you are going to be using

I will not go into setting up custom white balance for each camera you intend to use, but just be aware that there are slight differences in how each sensor "sees" the same scene, so using a tool like the Xrite Colorchecker Passport is essential to match image files from different cameras once you get to the point you are managing them with Lightroom 3 or Photoshop CS5