It could be any number of things ranging from unresolved issues prior to upgrading, a corrupt download or faulty installation. Have you done any trouble shooting such as Repairing Permissions in Disk Utilty, rebooting in Safe Mode, etc... How much RAM does the system have, that would all be useful information prior to guessing what your specific issue is. Please answer ALL those questions then we have a starting point.
First of all, thank you for your answer. So, I've reinstalled the OS X twice, I guess it can't be the real problem. I did the repairing permissions, that couldn't help either, but I haven't tried the safe mode. And I have 4GB of RAM. I almost forgot, the most typical situation when this screen appears, when I turn on the mac from sleeping mode. I don't know whether it matters or not, just it was a bit interesting for me.
Shame it didn't help. Did you try the Safe Boot that rkaufmann87 suggested:
Restart holding the shift key until you see the grey progress bar and once booted restart as normal from the Apple menu.
You could also try a PRAM rest, but other than that I'm stuck for ideas and think it may be a trip to an Apple tech.
- Shut down the computer.
- Locate the following keys on the keyboard: Command, Option, P and R.
You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
The symptoms you describe could very well be attributed to RAM problems. I would suspect the possibility of an issue with the RAM modules installed in your machine. The first thing I would do is ensure that they are installed and seated properly in their slots.
Here is some info about that for the late-2009 iMac... http://support.apple.com/kb/HT3918
Also, I believe the Late-2009 iMac shipped with a set of OS and Application restore discs which included an Apple Hardware Test application. http://support.apple.com/kb/HT1883
I suggest you run the hardware tests, particularly the RAM module tests and Video or Graphics memory tests.
If you don't have the Apple Hardware Test app, use something like TechTool Pro ($).
Perhaps someone else can recommend another hardware test app.
If the RAM checks out ok after several runs, and nothing comes of the graphics hardware tests, then the issue may be software related and you'll have to troubleshoot along that line.
I hope this is helpful.
Hi! Actually, when I had Lion, I had some 'freezing' problems. I thought it was a RAM problem. That's why I tried to check them in their slots, so maybe I didn't put them back properly. I'm gonna check them again, but I think it's not the real problem, maybe the RAM itself is the guilty one. So I've just run the Apple Hardware Test application you mentioned, but it found everything perfect. So after all, I think this whole problem is a software issue, just I don't know what to do about it. Can you recommend a way to start searching the software issue?
I think it's software related. Had the HD replaced, same issue. deleted a couple of apps, same issue. I also had issues with connecting my Jabra Halo 2 headset. Found soundflower, uninstalled, same issue. Found out that some people reported some sleep/wake issues with the new Bongiovi audio enhancer. I have/had the old version running as addition in iTunes that is no longer supported (unknown to me), uninstalled, deleted all relevant pieces in the library, reinstalled Mountain Lion, and hey presto, all runs like a charm for days in a run. IMHO it's worth checking whether you have any audio or video enhancers that might interfere with the regular OSX drivers.
I am having precisely the same issue and have tried everything above and all noted about this problem much discussed elsewhere.
I have also resorted to the restting the System Management Controller http://support.apple.com/kb/HT3964?viewlocale=en_US&locale=en_US
My Late 2009 iMac is the custom Intel i7 build with 8 GB Apple installed RAM and a recently replaced SEAGATE hard drive (under the APPLE extended fix arrangement). The OS was a clean install and has been upgraded to 10.8.3.
On appearance of the black screen the operating system appears to be running and responds to sleep and wake using the power button and occasionally shows the screen momentarily and sometimes briefly. Like others. the problem occurs on occassions and on those occassions persists. I also have another system purchased to hopefully get around this problem. I use this new system on the on the same supply ring main, a recent Mac Mini + screen. This sometimes has similar problems but much less often and the problems occur when the iMac has persistent problems. This leads me to think that there is a software and power mains supply problem.
I have also tried connecting the Mac mini too the mini-display-port of the iMac using the relevant cable and using the F2 toggle,. I can see the Mac mini screen even when the iMac has problems.
I live in London. our electricty supply comes from one company responsible for the national grid and pipe to customer. The billing and customer relationship is handled by a number of "suppliers". My supplier (EDF who took over London Electricity) recently included in their updates and materials, the procedure for notification of supply quality issues. This suprised me since I have not had issues of this nature to the extent of being naive on the matter. I have been told by others in the locality of similar MAC computer related problems. I have tried with and without surge supressor.
Whatever the problem, it is a nuisance to have an expensive and otherwise good iMac behave as it does. Any further input will be much appreciated.