Finder freezing up and unresponsive when I try to relaunch

I have an iMac 27" I just bought in April 2012. I started having a problem where my finder is freezing up and when I try to relaunch it, it's unresponsive. I can't force quit any applications and have to power down my computer by holding the power button. I thought it was the OS so I upgrated to Mountain Lion and I'm still having this problem. I repaired the disk permissions. I have searched everywhere and can't find anything to fix it.