hello I updated my mac paw Yosemite 10.10.3 and iPhoto does not open anymore, and all my photos were there .. What do I do ???

Did you got to the Apps folder and try to open iPhoto from their?

What exactly happens when you try to open it?

OSX 10.10.3 added the Photos app and it replaced the iPhoto icon in the Dock but yo can still use iPhoto by opening from the App folder.

See here: Get iPhoto 9.6.1 if you didn't update before OS X 10.10.3

Pete

What version of iPhotos is installed on your Mac?

In order to run on 10.10.3, you must have version 9.6.1 of iPhotos installed.