Switch to tty1 using Ctrl+Alt+F1
Login to your user account
opengl to Compiz active plugins list
dconf write /org/compiz/profiles/unity/plugins/core/active-plugins "[`dconf read /org/compiz/profiles/unity/plugins/core/active-plugins | sed -r 's/(\[|\])//g'`, 'opengl']"
Or reset the key to default
dconf reset /org/compiz/profiles/unity/plugins/core/active-plugins
If it didn't work, come back and reset all Compiz settings to defaults
dconf reset -f /org/compiz/
Switch back to tty7 (X graphic display) Ctrl+Alt+F7
Try login again.
ccsm applies changes instantly so may be it's a nice habit to make configuration backup before change.
Backup before change:
dconf dump /org/compiz/ > compiz.dconf
Restore if things went wrong:
dconf load /org/compiz/ < compiz.dconf
Sometimes it is helpful to monitor the changes:
dconf watch /org/compiz/