After latest Software Update my iMac goes to a prohibition sign on startup

[DonnyPauling]

iMac Info:
24" Intel Core 2 Duo, 2.66Ghz, 4GB Ram, running Snow Leopard, yadda yadda

The latest software update notice I received informed me the following new software was available:

* Performance Update (version 1.0)
* iMovie Update (version 8.0.5)

I told it to install the updates, after which the computer had to be restarted. Upon restart the computer seems to be restarting normally, ie: the bell tolls and the Apple symbol shows above the spinning icon. But after what seems like a very long time a "no symbol" aka "prohibition sign" takes the place of the Apple logo, and the spinning icon remains. Nothing else happens. To see the screen I'm referring to check this image:
http://donnypauling.com/images/prohibitionsign.jpg

Here's what I have done so far:

* I called expert case support and we tried a few things. The guy I talked to decided that I needed to use my snow leopard disk to use time machine to restore my system to the way it was before the software updates. He figured something must have been corrupted in the software update. I couldn't find my Snow Leopard disk so he emailed me instructions to follow when I finally found it.


* After finally finding the disk I followed his instructions and restored my system to an October 8th backup.


* Upon restart all was supposed to be well. That didn't happen. The same problem persists.


* Support is now closed, so here I am searching these discussion forums. One thread mentioned a similar problem and it was recommended that the person start in safe mode and repair disk permissions. Sure enough, my iMac starts in Safe Mode. I repaired disk permissions. Restarted the iMac. The same problem still exists.

Now what?

 

[Peace]

did you install an "update disk" for Snow Leopard or did you do a clean install of a "retail copy" of Snow Leopard ?

If you used a retail copy of Snow Leopard,or maybe even Leopard try to boot to the install disk and run disk utilities from it. See what is there and repair permissions from disk utility.

 

[pcs are junk]

do u have anything plugged in? like a time capsule or external hard drive? if u do take all those out, then click "option" when u start up ur computer and select macintosh hd, hopefully this will help.

 

[nigameash]

try repairing the mac os hd itself using the bootable dvd, something might have gone wrong with the update!

 

[DonnyPauling]

I ended up just having Snow Leopard reinstall itself. That, obviously, took care of the problem. And to my surprise, everything was still there when it finished.