Thanks for the add'l info. I haven't tried doorslam's chkdsk suggestion yet, but I plan to and will let you know what happens.
I have a dell Dimension 4600. I was able to boot to a Utility Diagnostics Area. I ran numerous hardware checks yesterday including extensive HD checks and everything passed. So I don't suspect hardware anymore (though I can't totally rule it out either).
My system still gets stuck on the Windows Is Starting Up screen. I did a Windows Repair thinking this would help (see previous posts) and it didnt fix the problem. I have not wanted to re-format the HD yet as there is data on it that was not back up that I wish to save.
I also suspect this could be a bad Windows update. My system was running fine until I updated Windows on 11/19. Thats when my trouble started.