Vista - dual screen vista

hi,
i have a dual screen setup with my laptop
the desktop was expanded to the left so the main screen is on the right of
me
now this has been working excellent, when i booted up my system and the
display was connected all was well
this isn't the case anylonger
when i boot up, the external display now starts expanded to the right so i
always have to move this in the display settings
now what is even stranger is that when i lock my desktop and then unlock,
vista is throwing the 2nd destop to the right again...

anyone knows how to solve this?
tia,
marc