After upgrade to 12.04, hanging in login screen

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http://askubuntu.com – Writing this from an older Dell Notebook, ugpraded to 12.04 32-Bit, which works well. My more modern Dell Notebook worked well for 1/2 day after upgrading to 12.04 64-Bit, now I'm having problems logging in: System boots normally, (Unity) can enter my password, the login-screen reports 'Logging in....', but that's the end, won't log in even after 30 minutes - it just stays on the login screen. Same for guest login. Console log in works well and quick. Checked Xorg.0.log.old, but didn't see an error message. The user:group for my home directory is correct. An fsck didn't find any errors. W (HowTos)