If you have a broken Cpanel Theme
you can reinstall it from a root shell.
cd /root
wget http://httpupdate.cpanel.net/cpanelsync/STABLE/x.tar.bz2
cd /usr/local/cpanel/base/frontend/
mv x x-old-backup
tar jxvf /root/x.tar.bz2
You may replace x with the name of the broken Cpanel Theme