Just today, after about a week of somewhat normal running (I'm a total beginner in Linux and the level of amazingly stupid problems I encountered made me go nuts), today my panel disappeared (the one with Applications/System menus, you'd call it taskbar in Windows). Also, Alt+F2 doesn't work and Ctrl+Alt+Backspace has no effect (I'd think it's supposed to do something).
I tried the solution posted here: Panel doesn't show at startup at Ubuntu 10.04
No luck, didn't change absolutely anything.

I also couldn't find the .gconf and .gconfd folders using search, so couldn't try that option. There were ones that had same names but without the dot though, but there were several so I didn't risk.

What could possibly be the reason for this? All I did yesterday was try to install some updates (another extremely dumb problem - doesn't allow to install even the official updates - "insecure sources" or smth like that, tried fixing it with some tutorials on the net but in the end it worked only for half a day and went back to refusal mode :@) and very few tools from the Ubuntu Software Center, but nothing that would change system settings just by installing it.