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Unity doesn't load, no Launcher, no Dash appears

I have been using 12.04 (wubi) since a week now and this is my 1st exposure to linux. Everything was going on fine till now , but today as soon as I updated through the update manager , docky gave a message that compositing is required or something, and i got an error window which asked me to report the error and then the update manager asked me to reboot.

After rebooting , i just get a blank desktop screen , no launcher, no toolbar. I have to restart with the power key. However if i login through Unity 2d everything is fine except the benefits of the 3d environment. I guess something got messed up after the update and i cant figure out which program or file caused this mess. I would highly appreciate if someone could help me out with this as I really liked working on ubuntu after windows 7. Thanks!

SOLVED-- Thanks @jrg for the link provided.. it helped me to come out of this mess. Actually some update of compizconfig made the unity plugin inactive did something to the Animation add ons , the one which you use for the burn effect etc. What i did was :

On the blank desktop Pressed keys Ctrl + Alt + T to bring up the terminal and typed ccsm This brought up the compiz config system manager, there i enabled the unity plugin and rebooted. Everything started working fine. But then again when i started the addons plugin ,everything went back to square one.. :( . This time pressing Ctrl + Alt + T also did not help. Then i tried Ctrl + Alt + F1 , it brought up a terminal or whatever u call it, and then i typed unity --reset , it did some resetting and in the end it showed some comositing done , I pressed Ctrl + Alt + F7 to come back to the desktop , and here it was , my old sweet desktop.. it had the animation effects too like wobbly windows, excepting the addons like the burn effect, i guess something got wrong with the last update of that addon plugin and now whenever i try turning that on , everything goes poof!! 6 hours wasted , but i guess i learnt something new.. not bad for an orthodontist i guess :))