Before anyone can help, they need information to work with. Basic stuff:
- What version of iPhoto.
- What version of the Operating System.
- Details. What were you doing when the problem arose?
- Did it ever work properly?
- Are there error messages?
- What steps have you tried already to solve the issue.
Anything else you can think of that might allow someone else to understand your issue.
With this kind of information somebody can develop a starting point for troubleshooting the issue.
Posts that consist of "iPhoto doesn't work. Help" or "iPhoto won't print" or "Suddenly I have no photos!!!!!!!!!!" mean that any helper is simply guessing. With information, s/he may be able to get your issue resolved sooner.
Cannot open iPhoto either, just did an update last week, today while trying to transfer photos, everything froze for good. Tried uninstallig and reinstalling, got back to the same old message:
"Your Photo Library is either in use by another application or has become unreadable
Shut down and restart your computer, and then open iPhoto again. If the problem persists, try rebuilding your photo library. To do this, quit iPhoto, and then reopen it while keeping the option and command keys pressed. You can also try restoring your photo library from a backup."