Currently Being ModeratedNov 16, 2012 12:57 PM (in response to skarbekb)
What system and iPhoto versions were preinstalled on your Mac when you got it?
If it was Lion or Mt. Lion then go to the App Store and log in with the Apple ID you used to purchase the Mac. Look under purchases and select iPhoto to reinstall it.
If you're referring to your iMac and the system was Snow Leopard or earlier you can use the Software Restore disk that came with your Mac to do a custom install of iPhoto. The disk will look something like one of these:
Currently Being ModeratedNov 16, 2012 2:05 PM (in response to skarbekb)
lost all my info
That tells it all. Unless you had a backup copy of your iPhoto Library on another drive your photos are gone for good.
In the future you should get an external HD and use Time Machine to backup your Home folder or the entire hard drive if the EHD is big enough.