BIG problem with new iPhoto

I have just downloaded the latest update of OS X Yosemite ( I have an iMac 2013). It did not download all of my photos. As a matter of fact - I have lost hundreds of photos that I was going to use for eBay listings.. as well as ancestral photos !. As reported by everyone else. I cannot access the old iPhoto. I tried the solutions listed here- however, in my App purchases - it lets me access all " but" the iPhoto. I am unable to "copy" it - delete it or anything at all. Subsequently, I cannot reinstall. I have looked everywhere and find no solutions. All the rest of the App purchases can be accessed. I have attempted to download older additions older iPhoto apps and that doesn't work...HELP!!!!

I also tried to copy the files but it will not allow me any access to my photos. The photo category has also disappeared from the file & download sidebar.. What gives..???

I am VERY upset. This is a decade of genealogy work to say nothing of the business aspect. ( By the way, I personally hate the new photo app.... I see no advantage for the iMac and it is visually quite bad.

Could someone please help me???

Thank you,

Jeannie