Problem with iPhoto

I am running iLife 11 on an IMac Desktop with Mountain Lion 10.8.3. Prior to the upgrade my iPhoto was working perfectly but now every time I try to open the iPhoto screen freezes and the whole operating system is frozen.The only way I can get out is by a 'force quit'.
I have a very extensive library and many albums with some priceless pictures.
One way I have been able to access the program (as before) is to open to the menu where I can rebuild the Library. This works but to do this every time is very time consuming.
Does anyone have any suggestions to stop this 'freezing' and have the iPhoto operate normally. Thanks

The very first thing to do is backup everything on your iMac if you have not already done so. Use Time Machine or any other method on hand. Next, boot your iMac to the Recovery partition (command + r), enter utilities, and verify the hard drive. Let us know the results.

I am not a very sophisticated user. After I back up do I shut down and then when I restart I use the Command -N keys. Thanks for the help.

Sorry that should read Command-r.

@Arjay37 If you're having some 2nd thoughts on how to do this, It's best if you let some tech guy do this for you. To be safer

Make your backup first. As I stated above, use Time Machine or any other backup method you have. Then, reboot and hold the command + r keys as soon as you hear the boot sound. Keep holding the keys down until you see the spinning circle. Once in recovery, select "Utilities" and run Disk Utility to verify your hard drive.