Ubuntu 14.04 freezes after latest update (18 May 2015)

After the latest update of ubuntu 14.04, I was able to log in to my account, but desktop refresh was extremely slow and toolbars were noisy. Clicking on toolbar icons does not react (actually, it took one minute to get the reaction). A reboot did not help. Restarting in recovery mode, choosing “failsafeX” entry did not help either. So, I suspected the installed nvidia driver (my PC owns a geforce 7300). The installed version was nvidia-304-updates. I gave nvidia-304 a try, but issue persists. I finally installed nvidia-173, which solved the issue.