The problem began about 3 weeks ago after Avast anti-virus update. Approximately twice a week system boots to Desktop with all icons but missing icons in the systray, and no icons respond when mouse is clicked plus CtrlAltDel doesn't bring up Task Manager. The only way the system will work again is to completely power off manually and restart. I've also noticed mup.sys used to be the last thing to load when booting to safe mode, but now there are 2 additional things that load after mup.sys that I think were added by the Avast update.
Could this problem be due to the Avast update or maybe an early sign of a failing hard drive? If it is due to the Avast update, should I switch to AVG, Avira or other anti-virus?