Just installed mountain lion and now my imac is in constant reboot loop. Any ideas?

Same. After completing installation it failed to restart and ended up in a constant reboot loop... Restart...Jargon screen (your computer restarted because of a problem....)...Apple...Spinning wheel....Restart.... I tried Command R and verified and fixed disk and parameters... Didn't fix.. I reinstalled Mountain Lion...Didnt fix.... I tried Command/Option/P/R and held it for 3 gongs... And restarted.. Hmmm it booted, all seemed fine, normal desktop appeared with icons for about 30 seconds... THEN it restarted and it's back in the reboot loop again. I'm out of ideas...

Safe mode (hold shift key at startup) gets me to Desktop... Doesn't resolve...but at least I can use my MacBook Pro now. Any suggestions how to figure out which application might be conflicting with the ML boot?

I have the same issue, I am working with apple support and as of right now they do not have a fix. They have mentioned that it might be caused from having a boot camp partition, but again they are not sure. I am glad to see I am not the only one having this issue, as apple support made me feel I was the only one. If anyone recieves a fix please let us know 🙂

For me I was able to boot into the lion recovery partition and verify my disk, reselct it as the startup disk and get back into lion. I was able to reinstall Lion from inside lion without an issue. So the issue does lie with Mountain Lion.

This must be a widespread issue. I am having the repeated restart loop also. The kernel panic jargon says the Mac OS isn't set.

Same problem here. Wiped my Bootcamp partition as it wasn't working anyway and same problem. Have removed all peripherals and still broken. Can boot holding down shift but that's all.

Boo. This looks like it's happening everywhere.

It seems that the problem come from graphic display driver or dual display driver. For my case, Mac Mini Mid 2011, I connect DVI->VGA to Thunderbolt and monitor but I use HDMI as main. It can solve this problem. My MBP 13" 2010 and 2011 does not hit this problem.

Clean install, in some case may solve the problem but not for me.

See this thread.

https://discussions.apple.com/thread/4135480?answerId=19051123022#19051123022

I m having same issue... tried everything but no luck.. I have Macbook Pro mid 2010. Now thinking to erase HD and start with clean setup. Please do help, if anyone got any idea about how to resolve this issue.

I installed it on a fresh partition so wiping might not solve the problem just FYI.

Thanks Rob. just dont know how m gonna solve this issue.

Good news is that you don't have to solve your issue. Bad news is that Apple will. Who knows how long that could take to patch. For now booting with shift held down should get you running. Other than that it's a reinstall of Lion I suppose.

Well, at least you can boot into safe mode. I can't.

Exactly the same issue, installed ML on my MBP (with built in encrypted SSD). I get to the user screen, pick me, it loads something and then the screen gets black again.

When holding Shift, it shows a loading bar, after the bar is full and the desktop should appear, it reboots again.

Tried repairing the disk in recovery mode (cmd + r), browsed the file system a little with terminal but couldn't find anything which helps me.

I'm currently writing in Safari IN recovery mode. I'm for additional 2 month on vacation, far far away from all my images, backups and whatever. I really need a fast fix for this even if it's just temporary.

Browsing in recovery mode is not a fix. Not at all.

All right, i solved mine. Now writing with Mountain Lion, but wow! That was a fight.

So, I saw that my mac is always restarting AFTER choosing the user, sometimes you could even see the mousepointer. So the problem might be in something that gets executed when the user signs in.

I booted into recovery mode (cmd + r), decrypted my HDD with disk utility and picked "terminal" from the utilities menu.

After browsing over a thread, a user mentioned he had problems with little snitch and trend micro, and exactly these 2 apps were also on my mac.

I removed them in

/Volumes/Macintosh HD:

- /Applications/

- /Library/Application Support/

- /Library/LaunchAgents/

- /Library/LaunchDaemons/

and everywhere else inside Library where could find leftovers. (I guess that's not so important but i wanted to make sure I don't miss anything)

After killing these, I rebooted the system and BAM! It is working!

Thanks finally everything is working Fine. Reboot with safe mode.. Delete every items from StartupItems under library folder. And reboot machine; and u all set for mountain Lion