Afterward, I installed Registry Mechanic, which seems to work without problem.
I have a P4, 600 GB; 500 MB.
I have updated (but hope not to have to uninstall and reinstall) drivers for both.
Otherwise, the computer seems to be working fine. By the way, I can backup commercial DVDs by writing them from DVD-RW -> hard drive -> blank DVD-R. I don't think the drives are dirty.