My D90 Nikon won't let me download on my computer?

I have a D90 Nikon camera and have been taking good pictures with it for a while and never had a problem. The other day I was just messing around and went to take a picture but when I went to look back at it all I saw was black. So I switched it to auto and the picture showed up. I just left it go thinking it would heal itself, but today I went to take pictures of my art (which I need tonight… Love when something goes wrong when you need it most) and they showed up on my camera like normal. Then I plugged the camera into my computer to download them but they wouldn't even show up. The rest of my pictures that were on there from a few weeks ago showed up and downloaded but the ones I just took didn't even show up. I switched to a few different memory cards but they kept doing the same thing. I even plugged my card into my printer (it's kind of like a memory card reader) and they didn't show up there either. I really need help. I'm scared my camera is broken… Is there anyway I can fix it by myslef or do I need to send it somewhere?

Did you switch to raw (NEF) format? The codec for this format isn't installed by default-you have to add it to your computer:
NEF codec http://nikonimglib.com/nefcodec/
Nikon downloads http://support.nikonusa.com/...il/a_id/61

The raw format is used when you want the original, unprocessed image the camera shoots, which is always higher quality than any of the JPEG formats. It is also specific to the camera, and therefore not standard, which is likely why your computer can't read it (yet).

Format the memory card before shooting. If the problem persists, try a new memory card.while you're at the store, get a cheap USB card reader too. Use that to connect your memory card directly to the computer. This method eliminates all camera to computer connection problems. To do the actual transfer, use Windows Explorer or (Mac) Finder for more control on what goes where exactly.