If your video card drivers
were updated then it sometimes causes this or at least that is when I have had it happen. Lately with Nvidia's last few driver
sets the icons have remained as they were when drivers were updated.
I would recomend a small program called "desktop icon position saver" and it probably can be searched for via yahoo or google very easily...it is the one I use and it is very simple...adds options to the right click menu to save and restore icon positions.
EDIT: I just did a search for it and I can't find it but I believe someone provided a link to the one I use in this thread earlier. The file name when you download it will be "dips64" for the 64 bit version. If you need me to email that version to you I can do so if you pm me with your email or email me directly at firstname.lastname@example.org
to request it if you can't pm me on this forum...I only have the 64 bit version.