My iMac 9,1 early 2009 is in the shop with Apple now because it would not start without using Safe Boot after I had installed Mountain Lion. Apple Genius Bar rep tested, HD Ok, reinstalled Mountain Lion, no help. He then wiped the HD, reinstalled again. Sill would go dark after the start-up wheel stopped. - He felt it was the graphics card causing the problem. After getting home, and doing some Googling, I started to encounter some articles about 32 bit - 64 bit issues with some of the older installed cards. I had the NVIDIA GeForce GT 120 256 MB installed in mine. Does anyone have access to a resource confirming whether that particular card is or is not compatible with Mountain Lion ?