Why won't my pictures show up?

I have a mac mini computer and a nikon d3100 camera. I took some pictures and video and wanted to import them onto my computer. I plugged in my camera with the chord and turned it on.nothing happened. I went into iphoto. The camera showed up, but all the pictures were blank. I tried to import them into iphoto but it just kept saying "error". I have tried multiple times, and nothing seems to work. On my computer i don't have a card reader so there's really no other way to import the photos. What should i do?

Sounds like a file format compatibility problem. Did you take the pix in RAW format? They need to be in JPG (JPEG) format.