I can still access the End Program box to shut down the computer. I can boot to a command prompt with the start up disk. I have tried extracting explorer, and several other files, from the original cab files, as suggested at the Microsoft Support pages. I have tried a scanreg /fix. Nothing seems to work.
Moving the hard drive to another computer and trying to save the data is a last resort. I don't want to lose some of the programs and registry keys on this drive. Is there anything else I can do?