Last night windows updated and restarted computer while blender was rendering. Today that file will not run - freezes blender if I try to load it and so does the immediately previous .blend file. If I could find the place where the preferences file is kept maybe I could fix this.
New information: Strangely I ran the .blend1 version of the file and it works. (I have lost some work because the .blend1 was an hour or two earlier and I can't remember how I did stuff)
In a previous 'freeze' problem I solved it by changing the names of the preferences.blend files in the Appdata location, so I thought this time it was the same kind of problem and that there must be yet another place where the data is stored, but maybe same symptom but different cause. Don't know what messed those files up (for both versions of blender 2.72b and 2.73)
Thank you very much for the effort you went to to explain.
PS- have changed windows setting to ask me before installing updates.