I did something silly I think.
I wanted to use dolphin as default file manager. So I used package manager (synaptic) to remove nautilus file manager (because Ubuntu makes it so hard to change the default file manager globally).
Now when I rebooted and wanted to login, I no longer see the Ubuntu unity desktop as an option to select from the menu at the login prompt. I only get into the gnome classical and gnome options.
I went back to package manager and reinstalled nautilus file manager, and rebooted, but still, when I get to login in screen, I do not see the unity desktop (no 2D option, nothing) it only shows 2 options, gnome and gnome classic. I tried both, but they are not the same as the original desktop I had which is unity, with the launcher on the left, and the dash thing, and the 4 desktops, etc...
(so confusing, so many desktops, and not even a way to find which desktop one is on at the time. Like right-click with the mouse on the desktop, should tell one, "you are using GNOME(classic)" or something.
Anyway, What do I need to do to get unity desktop? Do I need to reinstall 12.04? How? I am already on 12.04. I do not want to lose all the configurations I did.