Screen picture from current cursor position to lower right rapidly dark

[bullgard4]

Hello Forum,
since about 3 weeks my siduction computer shows an annoying bug: If the cursor is in a X window the screen picture jumps rapidly between two states:
1st state: normal: The whole screen picture is to be seen.
2nd state: faulty: The scrren picture is displayed only in lines beginning from upper left to the current cursor position. The lines from current cursor position to lower right are dark.
This is a regression.
If I am lucky the 2nd state does not occur for a while depending on exact cursor position.

Code: [Select]

~$ inxi -G -z
Graphics:  Card: Intel Core Processor Integrated Graphics Controller
           Display Server: X.org 1.17.1 drivers: (unloaded: fbdev,vesa)
           tty size: 157x58 Resolution: 1280x800@60.02hz
           GLX Renderer: Mesa DRI Intel Ironlake Mobile GLX Version: 2.1 Mesa 10.5.5 How to fix this?
bullgard4