problem with display breaking up

[Lisi Reisz <lisi.reisz@gmail.com>]

A client is reporting the following problem:

"The break up of the picture always occurs after I have just logged in 
and then click the mouse cursor onto an icon such as icedove or 
iceweasel"

"When clicking the mouse on an icon eg.for icedove or iceweasel, the 
picture fragments sometimes."

We have more or less excluded the monitor.  File corruption is not unlikely, 
given that he has been handling a mouse problem by turning the computer off 
at the wall.  The computer eventually failed to boot, but that has been fixed 
with an fsck.  I have fsck'ed every partition on the hard drive.

Do I try installing another video card?  But it feels like a software problem.  
So where next?

The mouse problem has been fixed by using a different usb port.

I have googled and got nowhere.

Any ideas where next, please.  Try a "new" video card to eliminate it as a 
possible cause?  And have video card driver problems. :-(   

Lisi