Now after a little over 2 hours the screen waked up again.
The screen was not black, but silver.
The graphics card is a NVIDIA, where I have the VGA connected to one monitor, and
via a DVI to VGA adapter another monitor is connected.
I have encountered, that something is slow, and I have seen it a while.
The DPC is ok, and also the CPU load measured with Process Explorer.
I have defragged the computer, and yes, I have ran all what O could get aware of
to have a clean computer.
BUT I might have overseen something.
CAN it be the Grapichs Card ?