I have an update. I used the windows restore program to return my computer to an earlier config. Everything worked fine.
A few months ago I got a Logitech Cordless lazer mouse.
It works fine with Sketchup except I wanted to customize one of the keys so I opened the Setpoint 4.0a2 program and modified the key. When I went to open Sketchup I got the same "don't know what your are talking about" behavior.
So my routine now is to open my Sketchup file, then open the setpoint software and modify the keys. Works fine except it's kind of a pain to do that everytime.
Has anyone out there had similar issues with the Setpoint program.
I guess my next step is to contact Logitech and complain. Their latest drivers don't fix the problem so maybe they aren't aware of it yet.
Thanks for the advice. I'm glad I didn't go and mess up my registry.

Everything was fine for several years, and then when I didn't use Sketchup for a couple of months, the truuble began. I'm using Sketchup 7 free on XP. When I hit the Skethup icon, or double click a skp file, or even navigate to the sketchup 7 directory and double click the exe file. I get one second worth of hourglass and nothing after that at all. Total silence from Sketchup, no error messages. Task Manager doesn't record any increase in activity during and after the hourglass. Sounds like a windows problem but every other program I use is working fine.
I even uninstalled SU and reinstalled it from a clean download.
Dare I mess with my registry?