I haven't posted for a few days - I haven't wanted to go near my computer. I have deleted my whole iPhoto library. No-one told me that it was kept in the Pictures folder!!!
My computer has been telling me for ages that the startup disk is full, so I decided to delete some pictures and documents I had scanned and no longer need. I trolled through the folder and thought they all had jpg on the end, not noticing a little icon that said iPhoto library.
I think I can retrieve it from a backup, from a few weeks ago because the backup has not been going well either, but I still can't open all the pictures, so I think I may have to delete other stuff - I hope that is the problem.
I haven't been game to try it yet, will need hours to go through it properly and make sure I don't delete other important stuff! If that doesn't work, I'll have to get professional help. More time and money wasted. But worth it if I get my photos back.