Comments inline...

"wernertk" <wernertk@discussions.microsoft.com> wrote in message
news:9CDDE490-0824-41DB-B9B0-DFAB3CD603FF@microsoft.com...
> Thank yo so much for your time looking into this :D
>
> I've been thinking the whole day what I did to have caused it. I was quick
> to give SP3 the fault, and realized that this occurred about 2 days after
> installing it. So SP3 is not the problem.
>
> The only thing I can think of was I used a tweak program (PC Health
> Optimizer) to hide a drive in My Computer called G:. This drive was created
> by installing a Canon MP520 Printer, and seemed like a useless entry for me.
>
> So I think the problem started turning the printer on/off and it could not
> display the G: drive.
>
> I only tweaked the hiding drive, and removing "Short-Cut to..." in the tweak
> program.
>
> So when I right-click the Start Button and click Explorer/Open, I don't get
> the '(null)' error. It's only when I use WinKey+E, right-click My Computer
> and clicking Explore. Maybe It's pointing to something in the registry that
> My Computer should show, but can't. I'm gonna do some system restores, to
> see if it fixes it :p

Your last paragraph is what I was looking for. When I perform the same steps
nothing happens except a screen blink since the folder tree is already expanded.
I assume that your folder tree is not expanded, if so, what happens when you
click on the + icon next to My Computer?

BTW, if you do any system restores, you'll most likely loose the registry tweak
you did to restore the Winkey+E function.