Are you regularly making backup copies of your Mac and of your photos? Your must be a very old model, if it still can run MacOS X Leopard. Sooner or later it will fail completely, so I would prepare for such an emergency and keep a copy of your iPhoto Library on an external drive.
What has changed, before you could no longer open iPhoto? Did you just import new photos?
You may want to check, if your Macintosh HD is full. It might explain, why iPhoto is crashing. In that case try to fee some storage. iPhoto may also be crashing, if you imported a damaged photo or video, that is causing iPhoto to crash. In that case you have to delete the photo and remove it from the iPhoto Library.
If you cannot find a specific video or foto that is causing iPhoto to crash, it might help to repair the iPhoto Library. But you have to make a backup copy of the library, before you try that. And you need to have plenty of free storage on the disk with the iPhoto Library.
Then try the fixes as described here by Old Toad: my iphoto 7.5.1 on Leopard 10.5 ox keeps … - Apple Community
I cannot test this any longer on my Macs, sorry, my old PowerBook with Leopard refuses to start up.