If Cyberhawk's solution does not help:I had a similar problem a while back. An application (I don't remember which) failed badly and spewed a massive XOrg log into my home folder, causing my /home disk to run out of space. As a consequence of this, when I would log in the gnome-panel would not work (with the same symptoms you are describing)
Deleting the logs and logging in again fixed the problem.
