XP T42 dual display problem: clone mode become extended mode

[lynnS]

Here's the story:

1) Installed Norton 2009 upgrade

2) Display became erratic .. sometimes there, sometimes very dim

3) attatched external VGA monitor

4) disabled presentation manager so FN+F7 should toggle mirrored displays

5) Have screen save enabled



What happens:

Periodically system changes from "mirrored display" to "extend desktop to this monitor". This is unsolicited. Sometimes the display is the "primary", sometimes the external monitor shows up as "primary" display. Most often, this change to "extended" happens during Norton virus scan. I have turned off the "Idle Scan" option.



There may be several things going on .. inverter card going, back light failure .. but why is the monitor mode changing?



Display mode after boot is unpredictable.



thanks for any help.