Mac doesn't Boot or Safe Boot or CD Boot only freezes on Grey screen


Hi to all...
My problem is that the mac [early 2008 iMac] it wont boot in either of the occasions that I mentioned. Suddenly today everything frozen except cursor, then the screen flickers and I shut it down in panic.
After this the mac will freeze at the start grey screen/ spinning wheel and the fans will start to go faster.

I have tried to:
/reset the nvram-pram option
/ hardware diagnostics [everything ok]
/ safe mode [dont boot]
/ unplug all peripherials except keyboard
/ installing the original RAM modules
/ boot from the install OSX disk
/ single user mode /sbin/fsck -fy command,
all of the above without result.
If somebody has an idea would be appreciated.



Try an SMC reset: Unplug ALL cords and connectors. The reset happens as soon as there is no AC power available. You unplug everything, in the event that an external device provides some power back into its connector.

When you booted to the installer, does the hard drive appear in Disk Utility?
Be sure to try a Repair Disk then (not Repair Disk Permissions)

Check that the air inlet on the back is completely clean and clear. That's the small round opening directly above the AC power connector, just below the hinge.
Boot into verbose mode, by holding Command-V. You can release that when text appears on the screen. It will appear similar to single user mode, but continues to show the various services that start up. If the boot stops, the last text may help determine what's happening.


You mentioned Apple's Hardware diagnostics worked & everything was OK. You also said it won't boot to install disk. Humm!

If it were me, I'd get Alsoft's Diskwarrior ASAP. Not cheap, but the very best repair tool available.


Hi again
Tried the SMC reset but no luck. With verbose mode it doesn't freeze at the same line of code but between two lines that are close, i will write exactly wich are this 2 lines:

/prl_hid/ Parallels HID Helper started
/drv/ HypIoctls.c:777 Ioctl VT-d status:0

I have never managed to boot the installer from the install disk and try the disk utility, it always freezes at the grey screen... sorry I meant before that I have tried but without result, meaning that it didn't pass the grey screen. My bad.

About the diskwarrior, is that meaning that is a HDD problem for you SGilbert?

Thanks guys for the help so far. :)

Oooo and also I cleaned the vent on the back... the best I could though...


I am running snow leopard 10.6 since more than a year or so, and the mac was running flawless. It was very sudden what happened. Does the onboard battery play any role in the whole situation, I am asking because is already a 4 years old machine? Also I if I will need to reinstall or format the HDD this cannot happen if I cannot run the installer. DEAD END


Try to boot to your installer, using this method:
OS X installer DVD in the drive.
Restart, holding the Option key.
Choose your installer DVD from the icons that appear, then press enter.

That should get you to boot to your OS X installer. Give it some time, even if it appears to stop booting.
I would likely give up after about 15 minutes, but 30 minutes would not be unreasonable.

If you can boot to the installer, I would suggest just running the installer, and let the system reinstall. It will not erase the hard drive, but will do something like an archive & install, installing a fresh OS X system on top of your existing software and files. Generally, it's a safe way to reinstall without losing your own files and apps.


Just tried with the option key as you mentioned and after a while came the black box [kernel panic] in the middle that says in few languages to turn of the computer. It looks bad I think.
I tried also to copy some files through the single user mode in a flash disk managed to do but some very important files aren't in english so mac cannot read them to copy them... maybe if I manage to copy this important files I can do after a format from the single user mode to see if it will work


The kernel panic may mean an incorrect OS X installer disk.
It's more likely an indication of a hardware problem, so (absolutely) try a memory reset again.
The memory sticks can sometimes need much more pressure to seat properly than you might expect.
I like to swap the memory sticks between slots, then press firmly, then alternate a firm push on each corner of the stick. I use a flat-tip screwdriver for that.

Can you still boot to the hardware diagnostics (that you already said "everything OK")?
That's the test the runs when you boot while holding command-D
Be sure to run both the standard test, and the extended test.

Do you have access to ANOTHER Mac?
You should be able to start up your iMac to Target Disk mode (by starting while holding a T, until you see the floating firewire icon on the screen.) If that works, you can connect through the Firewire port to another Mac, and your iMac will mount on that Mac as an external hard drive, giving you the possibility of backing up the files that you need. The text language of a file is actually not relevant to copying the file.


-I have checked the RAMS they are ok positioned.
-The hardware test both extended and standard finds "no troubles" as it says [made the extended 2 times in a row].
-Diskwarrior DVD doesn't boot.

Another observation is that if I let it to boot until the spinning wheel gets stuck, and then I push the power button for a shut down [but not long enough something like for 1 second] it puts the computer to sleep [probably] and then when I press the power button again or I press any button on the keyboard it wakes up showing nothing but black on the monitor, then if I press any button on keyboard it makes this hollow short sound, each time I press a key. Its like the OS is loaded on the background but I don't see it.

I tried to boot from snow leopard install DVD and comes the kerenl panic [snow leopard IS installed on the machine]

Don't have access to another mac at the moment... unfortunately



I wanted to add that when I press the option key it shows me the HD and the install DVD if I have it in the tray, and I can choose to boot from any of them, even though that doesn't happen at the end.


Hi again, I have found another mac to connect in target mode. First I tried Target boot mode, and i've managed to see my mac desktop with my programs my files and everything else. The mac though was taking too long to boot, and too long to make basic operations [copy/paste/open web browser], plus it was freezing every minute or so for a while. So after this test i booted in target mode again seeing my HDD from a healthy mac. I've repaired and formatted [HFS+] my HDD.Trying after to install a fresh snow leopard OSX from a DVD after 12-15 minutes the thing froze again giving me a kernel panic. After I run the diagnostics again extended and short, "no troubles found" message showed up at the end. Now vertical greenish lines appearing all over the screen.
It is very bad as it seems. Do you think is graphics card or logic board or anything else? Do they need replacement?



The hardware test does NOT do a really thorough test of the hard drive, other than to "see" the hard drive, and that the hard drive BUS seems to be working normally.
That would be my first suspicion, judging by the freezing that you experience.
So, I would recommend that you try replacing the hard drive.
HOWEVER, the "interesting" green lines all over the screen may indicate worse problems.

So, could still be a bad hard drive.

You said that you formatted your hard drive. That means you completely erased it, correct?
So, you could try erasing again, with the option to write zeroes to all blocks. That action can (sometimes) resurrect a slow hard drive that has problems with some bad blocks on the hard drive. The "write zeroes" option will "spare-out" or bypass bad blocks, and might help get you working better. That's assuming the problem IS the hard drive. The "write zeroes" can take quite a long time, easily an hour or longer just for that operation. And, if you choose a multi-pass write (which is really hard on a drive), can take overnight...

If you don't want to try that, then DO try replacing the RAM, just as a test to see if your Mac boots and runs better.

And, of course, the green lines that now appear....
The video card is replaceable, but perhaps not an economical thing to do. When there's no warranty, a video card is a lot of labor (it's mounted on the _back side_ of the logic board, which means a major job (lots of labor time)
And, even at that, it may be 50-50 that it's the logic board all the time.

I would take to an Apple authorized service shop for a good checkout (or at least a question or two)


Thanks DeltaMac I think there is nothing more to do, through this post. I bring it over an Apple authorized service shop to see what's going on.