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The past two mornings, the display on my iMac wouldn't come back up when clicking the mouse or keyboard as it has for the past 3 years.

The curious thing is that when I access it through Finder on my laptop, I can browse the iMac's files. But when I try to "Share Screen," it just hangs. Same when I try through the remote login service, logmein.

So the HDD is awake and I can hear it being accessed. And I can't bring it back up unless I hard shutdown the computer. This isn't happening during the day when the display goes to sleep; only after i goto bed and it has been asleep for a prolonged period.

  • I've had two iMacs over the years (a 24inch Core Duo Model 6,1 -the white plastic one-) and one of the first 20 inch with metallic case (a model 8,1 I think it was) and both had display problems: not waking up from sleep -the display, not the machine per se-, ghosts, dancing pixels. In both cases the problems were due to overheating GPUs. On the 6,1 the GPU is on a separate daughter card and although difficult to replace -and re apply thermal paste- it was doable. The other one I just sold. Good luck. – cucu8 Feb 14 '14 at 21:21
  • Thanks. What did you use to confirm it was the GPU overheating? iStat menus which can specifically monitor the temperature of different hardware components. If that is sufficient to check, what temperature should the GPU optimally be at? – Stuart Kuredjian Feb 15 '14 at 2:08
  • I did not have iStat back then and I do not know what the reasonable range is. I just ended up there through a process of elimination: 1-reinstall clean (no luck) 2-find & install new Apple specific drivers for the GPU (no luck) 3-use smcFanControl (which did appear to alleviate the issue) 4-Tear the machine apart, change the GPU - problem gone. All this was predicated by the fact that checking the forums somewhat consistently pointed to an overheating problem. The steps above where done for the model 6,1 which like I said has a "replaceable" GPU card. – cucu8 Feb 15 '14 at 10:01
  • On the 8,1, once the display started acting up I just tried smcFanControl and that again alleviated the issue, so I just sold it (for scrap, I did not fool the buyer, mind you :-) ). – cucu8 Feb 15 '14 at 10:03

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