I updated my 24" iMac (2.4 GHz Intel Core 2 Duo) to 10.7.4. Initally everything seemed to work well for a few hours but then for some reason it started to become slower responsively and closing a few apps helped a little. Getting back on the system in the morning the system was still very slow so I restarted the system hoping this would clear things up. Unfortunately, now I can not log in to the system at all. Everytime I put in the password at the Login Screen, the screen goes white for 10-15 seconds and then it goes back to the Login Screen. I tried resetting the password & permissions without any change and then tried resetting the passoword for root but this did not work either. Wanted to try to reset the Setup Assistant but the .AppleSetupDone file does not exist on my drive. Other than restore my drive from a very old backup, what can I do?