Q: I cannot quit iPhoto, shut down or restart my computer.

You will not loose any photos, click on the Apple logo up top, then select force quit, find the iPhoto app click on it the click the force quit button. 

Actually Force quitting is dangerous and may cause library corruption and should be used as a last result - any idea why you can not quit? What strange happened? What did you just do? any other information? How long has it been impossible to quit?

Force quit may be required but best to explore first

LN

If you have a problem with your iPhoto library you can rebuild it, take a look at this link, http://support.apple.com/kb/HT2638

If youu do a rebuild be sure to pay attention to the note in the first aid page that ecommendes you backup first - never do a rebuild, and update or upgrade withou first making a good backup

LN