Unity doesn't load, no Launcher, no Dash appears
I have been using Ubuntu 12.04 for a few days now. It worked perfectly until today, when I tried to do the following:
Using the Software Center, I tried to install Scilab, a scientific computing software. As it was being installed, I was trying to multitask, during which I realized that it was taking up too much RAM. In fact, it was way slower than multitasking in my Windows Vista. It didn't appear like the software installation was going to proceed, let alone end. So I pressed and held the power button to shut down the computer (first time I have had to do this for Ubuntu). When the computer restarted, it was unusually slow; and I logged into my Ubuntu user profile as usual. And then the computer didn't go past the wallpaper. No icons, no menus, nothing -- just my wall paper for half-an-hour.
I have an online assignment that's due. Please help me with this. Thank you.