After Update to Mac OS 10.10.2 grey Display and Stop symbol

Startup - Gray, Blue or White screen at boot, w/spinner/progress bar

Startup - Gray Screen

Startup - prohibitory sign at OS X bootup

Startup Issues - Resolve

Startup Issues - Resolve (2)

Startup Issues - Resolve (3)

Same problem here. Major Disaster – Seems to be Trim Enabler related. Recovery instructions from Cindori http://www.cindori.org/forums/topic/ssd-upgrade-yosemite-and-te-help-needed/ don't work with 10.10.2. I am now reinstalling the system. Sigh.

Thanks Bim2 - you saved me.

Luckily for me the instructions from Cindori did work on 10.10.2 on my iMac

Just adding a data point, my Dad's Late 2009 24" iMac had this issue with the 10.10.2 update. I reset the PRAM, ran Verify & Repair from Disk Utility, and ended up doing a restore from backup. Thanks to Time Machine there's no huge loss, just hassle and time :-/

So, there are a few problems with permissions. Restart the mac pressing the alt key and enter into the recovery menu. Open disk utility. Select the mac partition and hit the repair disk permissions. When the repaire is finished, restart the mac normaly. Have fun.