To clarify, I have not been running a Spybot SD resident process. I ran one scan and used the Immunize tab.
I have been able to boot in regular mode if I first boot in safemode, then in avast! UI, schedule a boot-time scan and hit the restart option in the UI. Upon completing or canceling the boot-time scan, the boot completes and avast! is loaded.
For this fix, I went through the sequence above to boot in regular mode. I used Spybot SD, Immunize tab, Undo button to remove "passive protection" from items. I downloaded and ran the McAfee removal tool, and hit restart on the tool. Windows shut down and restarted, and the boot hung again at the flash screen.
I then booted in safemode and uninstalled avast!. I rebooted twice in normal mode and then reran the McAfee removal tool. This time the boot after restart ran through and booted in normal mode. I reinstalled avast! and got all the updates. I restarted and normal mode booted well. I thought it might now be fixed, BUT, to be sure, I restarted again and the boot hung at the flash screen.