I've finally got round to installing Yosemite on my 2009 unibody Macbook pro, and to be honest I'm already regretting it... For the last 45 minutes it has been stuck on the installation screen saying "About 2 minutes remaining" and the fans are spinning fast. What is the best thing to do? Force power off or else's emit until something inside melts? How likely is it to corrupt the installation if I force power off? Thanks for your help.