Can't start OSX aqua - only Darwin (after 10.4.8 update)

Question

Hi everyone,
I updated my system sofware last week before leaving town. When I got back, I found that my computer will only boot into the Darwin command line prompt. I've looked around a bit and it doesn't seem as if anyone else has had this problem (in relation to this update). So I'm guessing that there just happened to be some problem when I was updating.
So far, I've started up with the tiger CD and done permissions and disk repair; I've started up off the hardware diagnostic CD (everything checked out fine); I've zapped the pram; I've run a permission repair live in Darwin (just to be sure); I've run fsck (which confirmed everything was fine); booting up in safe mode doesn't work (it behaves exactly the same as with out safe mode, only it might take a bit longer); I've tried starting OSX from darwin (with the same results); and I've restarted with nothing but the power cord attached.
When I start up I get the grey apple screen then it starts to load the GUI (working mouse and a blue background). Then I get the spinning gear on a blue background followed by a Darwin login prompt. In Darwin, everything seems to be behaving normally.
I just discovered (thanks to verbose mode) that there is a crash in the SecurityAgent every time the GUI fails to load (at least on startup). So far, this means nothing useful to me.
I'm enjoying learing more about Darwin and getting to know my computer better, I just wish I could get aqua to start!
Maybe there was a spontaneous hardware failure that coincided with the sofware update - that the diagnostic CD didn't catch? I don't (as of yet) have a different ATA100 HD to pop in, install Tiger on, and see if it's a software issue for sure. Maybe there're some things I haven't thought to try yet. I would be appreciative of any help or suggestions that anyone might have for me.
Thanks (in advance) for your wisdom.
Sincerely,
Nathan
eMac (2nd gen)   Mac OS X (10.4.8)   1.27 GHz overclock

Answer 1

This all happens most likely due to a corrupted key chain (entry).
For instance, if you choose to keep your local Airport password stored in your personal key chain it needs to be accessible by the private Apple Airport Framework used by the network preferences. If this by any means, is not possible - the automatic login into you Airport WiFi network cannot take place.
All you have to do to get this fixed is:
1) Launch your Keychain Access Application located at: /Applications/Utilities
2) Open the Keychain First Aid (under the Main Menu: Keychain Access)
3) Set the Radio Button to Repair and enter your Keychain Password (most likely your personal password)
4) Start.....
Now after your personal keychain (name=username) is repaired it might be listed double in your Keychain List Window (it depends how you've setup the keychain). If so, NEVER DELETE ONE OF THIS ENTRIES because that's obviously a cosmetic bug in the Keychain Access Application but not harmful. Just look in your local Preferences Folder, locate the file "com.apple.keychainaccess.plist" and thrash it. Re-launch the Keychain Access Application and there is only one again.
Restart your Mac and........
After all I think anything should be back up to how it supposed to be. :-))