Thank you for your reply.
The complete set of specifications of my system is listed in my profile.
And now to the details of my current problem: My win7 ultimate system behaves strangely. When I do some typing, the screen shutters. When I type, the active window is replace by another one without any clear rationale, when I type, only part of the text gets typed, etc.
I ran an analysis by TuneUp Utilities 2012 and got the following hint:
Windows reports that the "NVIDIA PORT IO Control Driver" device is not working properly.
All I found of NVIDIA products on my task list is a display driver for NVIDIA 9500 GT, which functions with no fault.