Cant' play video in i-photo anymore: worked well yesterday

Question

can't play video in i-photo anymore: worked well yesterday

Answer 1

First download and install QuickTime Player 7 for Mac OS X v10.6.3 or later.  Launch iPhoto and try the videos again.  If still no go give this a try:   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. if it does try the following: 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 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.
Still not playing then apply the two fixes below in order as needed: 
Fix #1
Launch iPhoto with the Command+Option keys held down and rebuild the library.
Since only one option can be run at a time start with Option #3, followed by #4 and then #1 as needed.
Fix #2
Using iPhoto Library Manager  to Rebuild Your iPhoto Library
1 - download iPhoto Library Manager and launch.
2 - click on the Add Library button, navigate to your Home/Pictures folder and select your iPhoto Library folder.
3 - Now that the library is listed in the left hand pane of iPLM, click on your library and go to the File ➙ Rebuild Library menu option.
4 - In the next  window name the new library and select the location you want it to be placed.
5 - Click on the Create button.
Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments.  However, books, calendars, cards and slideshows will be lost. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.
OT