After last OS X update, my system became unusable. It boots to the login screen, but then mouse clikcs and keyboard strokes are not being registered. The cursor is still responsive and light sensor adjusts the brightness of the screen, so the system is not hanging. I tried contacting Apple support, but "We are sorry, we are currently unable to process your query, try again later" message appears for the last hour. So much for the legendary stability and quality of support.... Any ideas of how to cope with problem? I tried holding cmd+s while booting, but it does not seem to be doing anything.