Albums and folders are missing from sidebar.

point at the word "albums" and to the right click on the word "show"

LN

Move the cursor to the right of Albums in the sidebar till Show appears. Click on Show for Albums, Projects and Slideshows.

OT

Ok how about giving us some details - remember we only know what you tell us - no ability to see you, your computer or read your mind

We could make off the wall wild guesses for years

What versions of iPhoto and of the OS

What has most recently changed?

Have you deleted the iPhoto preferences (that would be a good step if you have not)

What else can you tell us about what is going on?

LN

Try the following:

1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your

User/Home/Library/ Preferences folder.

2 - delete iPhoto's cache file, Cache.db, that is located in your

User/Home/Library/Caches/com.apple.iPhoto folder (Snow Leopard and Earlier).

or with Lion and Mt. Lion from the User/Library/Containers/com.apple.iPhoto/
Data/Library/Caches/com.apple.iPhoto folder

3 - launch iPhoto and try again.

NOTE 1: If you're moved your library from its default location in your Home/Pictures folder you will have to point iPhoto to its new location when you next open iPhoto by holding down the Option key when launching iPhoto. You'll also have to reset the iPhoto's various preferences.

NOTE 2: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.

Then I unhid the Library even though my problrm was solved

Why did you hide the library and how did you do it?

You were referring to the LIbrary folder, not the iPhoto Library. My error. It's nice to have it visible in case you need to find preference files at some time. If you apply any system updaters you'll probably have to redo the process to make it visible again.