No menu bar and unity launch after upgrading to 14.04; ccsm cannot start

Yesterday I upgraded from 12.10 to 14.04 by do-release-upgrade.
Things were Ok after the upgrading.

However today when I logged into my account, no menu bar, no unity launch.
I tried ctrl+alt+F1 to open the terminal and re-installed Ubuntu-desktop, but it didn't help.

Then I installed compizconfig-settings-manager. But ccsm failed with the error message could not open display.

The only good news was that when I logged in as guest, the desktop worked fine.

What can I do now?

Updates:

First thank you all.

According to Upgrade from 13.10 to 14.04 no unity dash for default user special compiz config, I deleted ~/.config/dconf/user and ~/.cache/compizconfig-1 and the problem was solved.

I think this was caused by my own configuration files. And definitely bain's method will work too.

I opened TTY because I failed to run terminal by ctrl+alt+T. I didn't realize ccsm couldn't work in that situation.

Thank you once again.