Suddenly nothing appears on Ubuntu except Desktop background; Also super key, alt+tab has stopped working

Question

This is my weirdest experience with Ubuntu. I had upgraded from Ubuntu 11.10 to 12.04 many weeks back. Till y'day night everything was fine. When I started my PC today morning, weird things are happening:

1. "Alt + Tab" is not working at all, it appears as of only "Tab" is taken; I am able to open terminal using "Ctrl + Alt + Tab" (shortcut) though and move between workspaces using "Alt + Tab + <arrow>"
2. "super" (which has windows logo) key is not working. Typically when I press it, it displays "start menu" kind of stuff
3. It doesn't show anything on the screen except the background; Generally I used to see top bar where apps like skype, date/time, power setting etc. used to reside
4. Not able to see left side app bar, which displays several icons when mouse hovers on it or "super" key is pressed

I restarted my laptop but no luck. Presently I am going to terminal and opening everything using command line, e.g. "google-chrome &" and "eclipse &", which is very annoying.

I haven't touched any of my settings in several days or install any updates, except y'day I did "sudo updatedb" just to update the locate command. Please someone help in this regard.

Answer 1

Ok, I got it solved. From one of the Ubuntu forums, I found that there is something to do with Unity, I ran below commands and now everything is back.

sudo apt-get install unity
sudo apt-get upgrade unity
sudo reboot

[Note: However still few things are mystery to me. Why the things mentioned in question happened in first place?

I have a dual boot of XP + Ubuntu on a 5 year old laptop. In windows, I had 3 logins, with mine login being the primary one. I had installed a cisco vpn 1-2 days back and since then other 2 logins are not working. This problem has also appeared after that. Weird!]