After update my imac to yosemite automatically power off ifself.pls help

Question

hi friends , I updated my imac (24-inch,Early 2009) to yosemite and update was ok.after update i restart imac  then it is booting and showing apple log and coming to password page then automatically power off ifself. if i start with safe mode it is working fine. can everyone help me.

Answer 1

Hi.
You are running into a problem that many users of the 24-inch, early 2009 iMac 9,1's have encountered (including me).  The Sudden Shutdown Syndrome is the scourge of many iMacs and Mac Book Pros.
Unfortunately, I believe that the only solution is for Apple/nVidia to revisit their geForce Tesla drivers and figure out if the power management is correct.
In your case, I'd try this:
1)  Boot up your computer in safe mode and log into your user account.
2)  In the Finder menu, select Go > Go to Folder...
3)  Type: " ~/Library/Caches" (without quotes) into the box and press return.  You will be taken to the Caches folder.
4)   Select all the files in the folder and move to the trash (do not trash the folder itself).  At this point, just leave them in the trash...don't erase them.
5)  Go back to the Finder menu, select Go > Go to Folder...
6)  Type: "/Library/Caches" (without quotes) into the box and press return.
7)  Do the same thing you did in 4)  This time, though, you will be asked for an administrator's password.
8)  Restart your computer in normal mode and attempt login.
9)  If you can log to the desktop, you may delete your trash.
Hopefully this will get you into your account.  If it doesn't, you may have to do a clean install of Yosemite, go back to Mavericks, or wait for an update.
Good luck!