Ok, tried it on another PC now.

result is nearly the same. NO bluescreen, but the game hangs up.
So I don't think the problem lies in hardware.

Specs of 2nd PC:

Athlon XP 2000
GeForce Ti 4200 (latest drivers)
Windows XP Prof

It would be very nice if you can help me with this.
How did you test Pixels-function? You said it seems to work fine. Maybe I am too blinded from programming to find the "easy solution".

Greetings,
Dirk