When checking sound preferences It shows the sound stuck on mute, it will not let you untoggle, I reset PRAM and it worked then a few days later same issue, PRAM worked every other time I tried but now it doesn't, it will go to a blank grey screen for a few seconds then to black for a few seconds then back to grey and this continues with it never advancing to the apple grey screen until I release the buttons then it continues booting up but no chime sounds. Any one have any ideas on anything else I can try my iMac is just 2yrs old I am sooo bummed. Any advice from any experienced maccers would be appreciated! 😀