Hi .it sounds weird...it should be fixed with reinstalling OSX... but reinstalling from start... Check this but i guess you already did : https://support.apple.com/kb/PH22067?loc... also do a reset holding Option-Command-P-R keys all together before the gray screen appears. Continue holding these keys until computer restarts for 4 times, then release those keys and allow to restart normally.. Sometimes this problem can happening without reason at all and come back...
Hello again. Because my answer was not so detailed.... It depends of what OSX version you running. If its Snow Leopard i dont think you can do anything only to reinstall OSX as i wrote before.. Before that as final try put a suitable headphones jack at behind imac and do that 4 or more times and check at system preferences at sound if internal speakers appear .play with output volume bar and make some restarts.. Also try to restart at safe mode holding down shift till osx is loaded. then restart normal..If did not fixed then reinstall OSX.. If you running Yosemite or later check if airplayXPC helper is running at activity monitor..
I had exactly this problem with same imac because accidentally i deleted an essential file doing some testings.. reinstalling OSX will fix it but first take these files you want because will lost any personal files or serials.
Hi my friend! Of course the drive failed because of the bad construction of cooling in these desktops.I cant understand what Apple thinking when was making these all in one machines..Maybe is only for Antarctica? :) I have seen temps in hard drives more than 50c and continiously..They cant last like that..The most is 37c at continuous operation..Of course Western digital hd's can last longer than any brand( not the blue). The only solution is to install a third party software to control fans and the only one that is working as i said some months ago is : http://www.derman.com/iMac-Fan-Control Dont search anything else is not working like this at least for my mac. then join the two point connector together itsself. The next thing is to put the hard drive outside the aluminium case and put an fan from desktop tower on it with a case for external drive and then your hd will be work at most in 32c. That's it.
Put inside the old thermal connector (in case you will put again your old seagate hd) 2 cables with connectors like these they use in windows pc's for microphone on motherboards, put the black color on the first pin of WD hard disk closest to SATA connector In the lower (looking disc from above and connectors facing you) and the white colored cable next to black. Install fan control daemon and your finished. I played a lot with this and I find this is the best solution. Don't worry about hard disc, its running at most 37c without cooling. You can go then to fan settings and make them run as you wish. I have them in 2000 RPM on all.