At the end of the boot process, right after you see your desktop icons, the computer starts trying to access the A: drive . .the head is thrashing. This continues until you put in a floppy . .any floppy. The problem does not occur when I boot up in safe mode. I suspect a registry entry that causes this. How does one go about finding the source of the problem?

I would start by looking at my environmental settings. Look at the path. If a: is there it will get checked. Otherwise it is some kind of startup program. Look at your run and load lines in the registry.

Try clearing your recent documents list first - right-click taskbar, select "properties", it's on the "advanced" tab. If that doesn't work, maybe you've got a IE history item pointing at the floppy. Clear history from internet options.