restore Iphoto library

I was at my one to one training, and my portable hard drive got knocked and disconnected from the computer. The library needed to be rebuilt, but when it tried, it said the iPhoto was not compatible. The trainer said it was OK to redo it, but now when I brought it home to my computer, there were no photos. I imported my library from my hard drive, but most of my photos are missing. I know I have everything backed up. Can I do a restore that way. And if so, how do I do it?