Explorer not responding

From time to time, my startup hangs up. After the initial splash screen, I get as far as my wallpaper screen and the only activity after that is my cursor/hourglass. When I key in “Ctrl+Alt+Del” I get the Task Window, and see "Explorer not responding". I need to shut down again and restart. The machine goes through "improper shutdown detected" routine and the associated machinations, before restarting. I'm running Windows Me and Explorer 6.0. I've periodically gone through complete defrags; virus/spyware scans and cleaned up what little I found, but the annoyance persists. What are the possible causes and solution? Thank you - DRT

I re-cleaned my registry yesterday with System Mechanic 5, and so far I have not run into the problem. So far, so good. Thx