Hi Again Calmat
Many times one problem can have many causes. I have seen a member in Seven Forum with this problem due to conflicting software. Try a clean boot and see if it helps.
Troubleshoot Application Conflicts by Performing a Clean Startup - Windows 7 Forums
I did not read all the posts in detail, but this is just the sort of problem that a system restore may help.
Based upon everything that you have tried, I do think that it is a registry problem that can be fixed by manually adjusting the registry or a System Restore. There are many references in Google re registry and auto play, but I would be reluctant to use them without expertise in registry.