Q: OSX Lion + 2011 iMac 27'' + Video = Freeze

I'm new to macs. How do I go about uninstalling lion and reinstalling snow leopard?

I just bought a mid 2011 27 " iMac with 16 GB RAM, i7 Quadcore, Radeon HD 6970M 2 TB, 250 GB SSD, 2 TB HHD. I updated to Lion and started experiencing the same problems with freezes after viewing videos. I also noticed a freeze when importing and transcoding video clips with Aunsoft Final Mate. I also think that it randomly freezes at other times, For example, when I was trying to view system information, it wouldn't respond to mouse clicks on the More info... button for a couple of minutes. I am running a dual monitor configuration and am using a bluetooth keyboard, a bluetooth magic mouse, and a trackpad, all at the same time. I wonder if that might be part of the problem. But I had this same input configuration with a Mac mini and it wasn't a problem. Of course, I was running Snow Leopard. I also have Flash installed.

I'm fairly new to Mac and had hoped that it would be an improvement in reliability from PC. So far, it hasn't turned out that way.

Instead of replacing LION with Snow Leopard, you could use DISK UTILITY to create a small (25-30 Gb) partition on your HD, and install SL on that.  Just boot into SL whenever you use your Mac.  You can still read all of your personal files (music, video, etc.) that are stored on the LION partition easily---it's all on the same disk.

This is what I have done, since LION continues to freeze.  There is no work-around to avoid the freezes.  Apple must deliver a fix.  Once they do, just boot back into LION, install the update, and delete the SL partition.  I think this is a less disruptive solution than getting rid of LION altogether.  Retreat to Snow Leopard, wait for fix, apply fix to existing, unused LION partition.

If you need help doing all of this, just google it.  There are many articles demonstrating how to partition hard drives.

I would like to add to this string that my iMac purchased at the end of June HAS NOT BEEN UPGRADED to Lion and it's froze to the point that we don't even turn it on. I don't think it's a Lion issue. It started during Facetime, then videos now NOTHING. I've upgraded to Lion on my MacBook Pro and love it. I really wish they would give us direction on this. I'm paying on a iMac that I can't even turn on!!!!

My 27" iMac came with Lion preinstalled.  Now I need to buy SL just so I can have a working $3k PC... sigh.  I didn't even have this much of a problem when I installed Vista on my Windows PC.

had the exact same problem.... brought my 1 month old imac into store got it replaced with abrand new one lion preinstalled and have the exact same issue.

I took my iMac to a Genius and he acknowledged that many people are reporting the issue. My Kernal panic appears to sparked more interest so I am without my iMac until Apple runs through it's processes. I assume that we all should see a fix. Good luck everyone.

I'm not going to go through 35+ pages to find the original reply but I am starting to see graphical glitches in the menu bar and dock.

I have never seen this problem before. In fact, I've never shut down the computer or put it to sleep since the freezing issue. Restarted earlier today and now im seeing these glitches.

There's something weird with Lion.

Have it too...10.7 2.5 iMac

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If everyone would simply Call AppleCare and bug them to death, they will fix it. I've been in constant contact. Call, Call and Call again.

Call Apple technical support is useless, for I have called several times and just tell me to do a hard reset pram or erase all data from hard drive and reinstall Lion, it increasingly looks more like windows . It is just those times when a Mac was a gem. Today, a Mac is a very expensive windows.

What we should do all people, is asking for the money we've spent on lion. and return ourmac. I am sure that this does not happen with the iPhone or the iPhone.

What does not make sense is to buy a new Mac with super lion and you hang up every dayseveral times. This is a crock, and I think many people are frustrated with this problem.Apple needs to put an immediate solution. Apple is close to Microsoft. Apple knew this problem in the GM version, so it should not take to put a solution.

The story so far:

See this blog post, where I summarize the issue, and the suggested steps to fix it:

http://www.mcelhearn.com/2011/07/31/new-imac-lion-video-freeze/

I'm updating this post regularly as new information ariises. Save yourself the time of reading 35 pages and read my summary. And feel free to post comments, if only to add one more voice to the growing list of those affected.

This problem is hitting me as well on my new 27" iMac.

As others have observed it seems that the iMac's video something-or-other hangs at a pretty low level. Nothing other than the mouse is able to draw. Sound continues to play.

This has hit me consistently in two situations:

1. Playing a video embedded in Safari

2. Playing a video via iTunes

Interestingly, it is possible to SSH into a machine in this state though I wasn't able to learn anything useful via the command line while SSH'd into the stuck computer nor was I able to kill any processes to get the iMac unstuck.

Obviously you need to enable SSH ahead of time on the iMac (System Preferences -> Sharing -> check "Remote Login") and you have to know the IP address or hostname of the iMac, which may change from time to time if you're using DHCP, but "luckily" this issue is so easily reproducible by playing video that you can write down the IP address and get the iMac stuck for SSH diagnosis by watching random Internet or iTunes videos for a few minutes :-/

I'd personally be very interested to know how this problem made it into the Lion release code. I.e. was it somehow missed or was it simply tolerated with the intent to fix via an update. Either is pretty alarming given the reproducibility and severity of the problem.