Upgrade to new OS, but can no longer log in to computer

Question

I upgraded my iMac to Leopard and after the upgrade is complete, the machine boots up, asks me for a name and passwrd, but does not accept anything.
I tried resetting the user password using a startup disk, but same results. machine boots up, does not let me log in.
What should I do?

Answer 1

Wow, does this sound familiar. I got the same thing with a gray screen, a log-in area in the center that showed my correct primary account, and the right password clue (a password I've had for four years, mind you, and one I had successfully used over 30 times the day before for the installations). It was not accepting my password at all, and just literally shook the log-ing box like an earthquake on the screen, refusing any and all attempts at going around the problem. I couldn't get past it to get to my other drives, one of which should have been just fine.
I ended up having to take it in for repairs, and the repairman booted in from an external drive with OS, (another Mac would do the same thing - see this article for how-tos: http://docs.info.apple.com/article.html?artnum=306857
What the repairman did at that time was to go into Utilities and take out the password protection on the startup screen (which, btw, I had never HAD on the start-up screen before, and only used that password for logging in to iTunes, my dot-Mac account and security changes to the machine).
Once he had removed the password, I was able to get in and try to do an install again. I was able to do an upgrade install on only one drive - the original one. I had a conflict in headers on one RAID drive that using the disk utility and Drive Genius and other tools similar to Boot Camp did not solve. When I tried to install Leopard again, I ended up having icons and literally all the associated information (programs, photos, iTunes, etc.) disappear before my eyes - literally with icons disappearing from the screen as I watched.
I ended up having to nuke the entire system on all of my RAID drives, losing everything in the process. It has been working fairly well, except for some Email and other problems at times, after I nuked the entire RAID set down using the Disk Utility to erase the drives first for the new installation. Leopard would not even allow me the option of doing an erasure and clean install from the disk, btw, once I had the other problems start up. The ONLY way I could get it to work at that point, was to nuke all the HDs from Disk Utility. Real nuisance, but luckily I had backed everything up onto a 1 TB external before attempting an install.
Don't even attempt to install Leopard again once you get past the log-in problem, until you have backed up your information, or you could very well lose it all.
BTW, the Mac repairman told me that he has 12 machines in his shop at once, all with repairs necessary from the Leopard installation. Considering I've never had this problem, or anything like it with a Mac, and only have come to expect that with PCs, this is very disappointing.
Good luck!