[ubuntu] Upgrade failure at Alt F2

Every time I try to do the upgrade via update, I get as far as clicking Alt F2. An icon of three gear wheels appears, but then nothing happens. If I hit ENTER, nothing; if I double-click the icon, nothing.
On the second try, I somehow ended up installing 15.10, but -- it opened in the keel, and I couldn't get out of there. I tried Alt F7, but nothing. Finally, I reinstalled 14.04, but I am back to the same upgrade problem. I get as far as typing in 'Update manager' at the top of the screen and and I get the icon, then nothing.