Gnome panel and menu bar can't be clicked..!

Your gnome settings are corrupted some how. Instead of spending time debugging them all, your quickest solution is to create a new user and move over your document files. The other option is to try and reset the options for gnome:

From a terminal which you can get to by going Applications > Accessories > Terminal, copy and paste the following:

rm -rf .gnome .gnome2 .gconf .gconfd .metacity

This will remove all of your gnome settings and set them to the default settings. These files are normally hidden files and you don't normally see them in your home folder from nautilus (nautilus is the file manager that is shown when you go to Places > Home).

Log off and back on to apply the changes.

The solution to the problem was very simple

Click in the menu
"System"
"Preferences"
"Windows"
Then under "Movement Key"
select the radio button for "super (or "Windows Logo")

I don't know if this is the way it is supposed to be set or if it is backwards now (I never looked at this setting before) but my mouse now works correctly on Ubuntu 10.04

http://ubuntuforums.org/showthread.php?t=1512841

Try to kill and re-run your panel app process.

Can't run terminal?
If you are unable to start the Terminal (e.g. using a shortcut Alt+F2), but can run file manager,
you can find the Terminal in: /usr/bin/gnome-terminal (or generally in /usr/bin/*)

1. Search for a panel process (e.g. gnome-system-monitor > tab "Processes", search for something *-panel), for me it was xfce4-panel, for you it is probably gnome-panel

2. Run terminal

3. Kill all of it: sudo killall gnome-panel

4. Start it again sudo gnome-panel &

If you have Xubuntu, your panel app process is probably xfce4-panel, then, of course:
sudo killall xfce4-panel
sudo xfce4-panel &