mysterious vertical blue bar on the left edge of LCD

Hello. I have a PC with an LCD native to 1440x990 connected to the
second port (VGA connector) of my Radeon X1600 video card. It had a
problem of displaying a vertical blue bar on the left of LCD, and the
problem changed from occasional to always by yesterday since I restored
LCD to factory setting. The problem is vital as when it happen only half
of the desktop is visible.

In order to explain the problem I have to define two terms:

Desktop: What the computer intended me to see.
Viewport: What can be seen on the LCD. Normally viewport matches the
Desktop.

Description of the problem:

If you have an ordinary display, shift rightwards the desktop so much
that only 40% the desktop is still on the viewport, while the left half
of the viewport is black. Now add a blue vertical bar of 2 pixel wide to
the left edge of the viewport, now you get what I see.

Trying to find out the cause of the problem:

In order to exclude possible reasons:

The problem reproducible at 1440x900
The problem reproducible at 1024x768
The problem does not occurs at 800x600
The problem reproducible if I reboot to Windows 7 at native resolution.
The problem reproducible if I reboot to Windows XP, native resolution.
The problem reproducible if I switch from X11 to fb console on Linux
The problem does not occur at the splash screen of all above OS's.
The problem reproducible if I replace VGA cable.
The problem reproducible if I restore LCD to factory setting.
Asking LCD to auto-adjust would not get the display back to normal.
The blue bar is always blue despite OS's and color of desktop.
The blue bar is as tall as the desktop.
Can be identified by trying to shift desktop upward and dowward.

There is no way to adjust the viewport to contain the desktop, because I
can by maximum shift the display leftwards by 25%, while I need to shift
it leftwards 40% to get desktop to the viewport.

P.S.

I also see this problem in the past years on other computers before,
thus pretty curious what kind of fault can products such behavior.