I am currently running OSX Mavericks on a Late 2009 iMac. I have noticed lately that every time I restart my computer, I get the "bong" sound followed by a grey screen and spinning beach. My computer will stay this way (for hours) until I restart the computer again and put it into safe mode. Once my computer boots into safe mode, I am then able to restart the computer again and it boots normally. I have run disk utility and it says my hard drive is fine and I have run onyx as well. Has anyone else run into this? Any ideas as to what is going on? Thanks.