Went to work on it today, and it booted up just fine, no problems, no missing desktop icons, no slowness, no refusing to show files, etc. The only item in the Event Log was still the "The speed of processor x in group 0 is being limited by system firmware. The processor has been in this reduced performance state for 538964 seconds since the last report." on all 4 cores. I am sure the problem will be back at some point though. Meanwhile, it will be time for an image backup and other update items.