Q: iPhoto is very slow and crashes the system, how to fix?

  http://www.apple.com/support/iphoto/

that will link you to tutorials, help, iPhoto Community.

You really need how to repair and maintain your system.

I would go for an erase and reinstall from your backups if a simple Disk Utility and Safe Boot and Recovery Mode don't.

Your disk drive's directory, and the files, are corrupt and need to be dealt with.

Direct you to the proper forum for MacBook :

MacBook Series Forums

https://discussions.apple.com/community/notebooks?view=discussions

http://www.apple.com/support/macbookpro

Mac OS X Forum

https://discussions.apple.com/community/mac_os?view=discussions

This forum deals with a desktop/tower 65lb Mac Pro

http://www.apple.com/support/macpro

TimeMachine 101

https://support.apple.com/kb/HT1427

http://www.apple.com/support/timemachine

Mac OS X & Mountain Lion Community

https://discussions.apple.com/community/mac_os

https://discussions.apple.com/community/mac_os/os_x_mountain_lion?view=discussio ns

Recovery Mode

http://support.apple.com/kb/HT4718

General purpose Mac troubleshooting guide:

Isolating issues in Mac OS X

Creating a temporary user to isolate user-specific problems:

Isolating an issue by using another user account

Identifying resource hogs and other tips:

Using Activity Monitor to read System Memory and determine how much RAM is being used

Starting the computer in "safe mode":

Mac OS X: What is Safe Boot, Safe Mode?

To identify potential hardware problems:

Apple Hardware Test

General Mac maintenance:

Tips to keep your Mac in top form

Based on my experience with iPhoto and heavy photo library use:

Move all your photo images and the iPhoto library to Thunderbolt storage

Replace the internal hard drive with SSD

Upgrade to 16GB, 12GB at least, from what you have (4GB doesn't cut it, 8GB might get you by)

Upgrades for RAM and disk storage:

http://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3_133 3MHz_SDRAM

http://support.apple.com/kb/SP619 Apple specs are not always accurate, was based on what they knew at the time and do not get updated when more RAM and other upgrades become available.

So yes make sure you don't lose more files and data - the problems will get worse if not addressed, but instead of trying to "fix" instead try and start frolm the ground up with a more robust and powerful setup - and start with a clean install of Mountain Lion 10.8.4. Upgrades from 10.6.8 if that is what it came with, to Lion and then ML is neither ideal nor results in best OS performance and stability possible.

What exactly happens when it crashes the system?

Remember: we cannot see your machine. There are 9 different versions of iPhoto and they run on 8 different versions of the Operating System. The tricks and tips for dealing with issues vary depending on the version of iPhoto and the version of the OS.  So to get help you need to give as much information as you can. Basic things like :

- What version of iPhoto.

- What version of the Operating System.

- Details. As full a description of the problem as you can. For instance: 'iPhoto won't export' is best explained by describing how you are trying to export, and so on.

- History: Is this going on long? Has anything been installed or deleted?

- Are there error messages?

- What steps have you tried already to solve the issue.

- Anything unusual about your set up? Or how you use iPhoto?

Anything else you can think of that might help someone understand the problem you have.

Besides answering Terence's questions as a test  launch iPhoto with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it?

OT