Mountain Lion installation failed

Sounds like your hard drive may be experiencing failure. If your iMac came with recovery CDs you may want to run the hardware diagnostics on it. If you don't have those CDs, I'd recommend taking it to an Apple store to have them run a hard drive test. IMO, you will need to replace that hard drive. Data recovery can be iffy on a drive with hardware issues, but not impossible.

I am having the same issue, I can't imagine it being a bad hard drive. I just bought a new hard drive not even a week ago and successfully installed Lion on it with no problems. I need a fix to this as well, I can't get out of the installer!

Same problem, too. Working just fine beforehand. Hope to get some answers.

Same problem. Worked fine prior...

Same thing here. I was unable to run the disk repair (the button was inactive), so I tried to boot from DVD and now my iMac won't start up at all anymore.

I had the same problem. I'm taking it in saturday to see what the genuis bar can do. Everything has always worked perfectly on my 3.5 year old MacBook up until this point.

Mountain has sidelined my MacBook pro December 2008 pre unibody. The same condition as everyone responding.... APPLE HELP

Okay, I googled and googled and ended up doing this with my (still working) MacBook Pro:

http://osxdaily.com/2011/08/08/lion-recovery-disk-assistant-tool-makes-external- lion-boot-recovery-drives/

I succeeded to start up my iMac and then tried to do disk repair for my HD. I ended up with red warnings telling me that my HD cannot be repaired and must be erased. I kept on praying the ghost of Steve Jobs to make sure my Time Machine clone would be unharmed. Before erasing I decided just give it a try and clicked one more time the repair button. And suddenly I got all green and disk was successfully repaired. Just to be sure I did that one more time and then scanned the HD. Still all green.

Now I'm trying to upgrade to Mountain Lion once again...

I was having the exact same trouble and resetting PRAM resolved the issue for me. Hope it works for you guys.

I'm starting to be pretty sure that the root of all evil is the ML-upgrade file. I repair my HD, all fine, I try to install ML, it fails, I repair my HD again... I've jumped these hoops quite a few times now and no matter how many times I repair my HD I'm unable to install ML. But now I'm able to use my iMac (with Lion) again and I guess that's good enough for today. I guess next I'll try to download ML again and see if this file was corrupted.

I finally succeeded after resetting PRAM too. Thanks Jack!

I'm still looking for that Steve Job's magic. Still not working. Each time the DU says ..."can't repair this disk. Back up as many of your files as possible, reformat the disk,..."

Besides erasing the disk, any suggestions?

Same issue for me a second time through. I managed to get snow back and access to my computer by putting in the old OS x install disc, stopping the install and shutting down, then restarting. Worked twice. Apple has an issue here...

+1 Same problem after about 5 minutes of install on my '11 MBP 13" and then you start hearing the hard drive and then the installer complains there is a problem. No hard drive problems experienced prior to ML install. Should have waitied but was real excited. Now I have to wait and figure out how to fix this problem. Only if the new iMac was out, I could just buy that, restore from time machine, and be good to go while figuring out the MBP issue later.