Desktop disappeared! help!

[forfan forfan]

I am under debian sid, using xfce4.2.

yesterday, my xfce desktop was suddenly disappeared. 
wallpaper was lost, and right click with mouse, app menu was not shown.
why?

I try to change to root account. It seem that it is ok with other user account.
I also manually run xfdesktop in terminal, wallpaper was shown, but
mouse right click
still didin't  work.

anyone can help?

Thx so much