Desktop go away during normal activity.

hi,
I've a big problem with windows vista premium.
During the normal use of laptop, for example when I surf the net with
Firefox, I see that the sidebar missed, and missed also the desktop, the
windows key that open start menu doesn't work, so the only solution is
restart the system.
I made 2 screens of the problems.

Sorry if the words in the screen are in italian.

http://img259.imageshack.us/img259/4053/bo1wp0.jpg
http://img443.imageshack.us/img443/4668/boqr1.jpg


Many thanks, Rolando.