Ubuntu 12.04. Previously I had a working installation but several crashes did not shut down cleanly, and things began disappearing from the launch bars. I noticed that I had lost my admin powers when I launched Synaptic and a message pops up and says I can only look, since I do not have sufficient rights to change anything. After checking, I found that this was true - a user directory I had created previously was off-limits.

I have 4G ram on a 3Ghz dual core PC.

Re-installation has not helped - either clean installs or repairs. The only thing I have not done is format that drive. From my standpoint.