password doesn't work after archive and install

I was advised to do an Archive & Install, without preserving info to see if it would fix a weird slowness issue.

I just did the Archive & Install, and when it restarted, it showed my name and photo, but it wouldn't accept my password. I can't login. All I can do is restart or shut down.

I rebooted from the install CD. Same thing.

I rebooted in safe mode. Same thing.

Help!

Paula