OS X :: Prohibition Sign On Startup / After Latest Software Update

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.