iPhoto suddenly empty??!!

Hi. When I open Iphoto it says it has 0 photos!! I did have 2500!! in the finder in pictures the library is still there and it says the folder is 5gig...but when i click on that it opens iphoto and says no photos!!! this is a bit scary...any thoughts!! update...i just checked in desktop setting and when i choose photo library for my desktop picture all the photos are available there...but still when i open iphoto there is nothing! hmmmmm

Just hold Alt (option) while launching iPhoto, click the Select Library button and choose that 5 gig library.

hi, thanks, but when i do that it says no photos

Thanks - I had copied my iPhoto library from an old external to a new one, then ejected the original external. I thought I would get the "Library not found" dialog, but I didn't. This worked. Yay!