I've had all sorts of problems with my IMAC which is a mid-2011 model running Snow Leopard making it basically unusable. Tried everything to get it going again without success. So finally out of desperation and knowing I would loose invaluable photos and other files, I decided to just wipe it out and reinstall. That process took over 4 or 5 hours - it said it was successfully installed and needed to reboot so I said ok. But when it did it was the same problem as before nothing but grey screen. I am at a total loss as to why - if your drive is shot will it go ahead and install anyway? I used disk repair and was successful before doing the install. I'm ready to throw this $1200 computer in the trash.