How?
I have installed gnome-shell, though that didn't do it.
Previously i have removed compiz but it reinstalled itself.
Finally I went to .bitcoin and deleted everything except for blk0001.dat and blk0002.dat and restarted Bitcoin.
As soon as it started I saw the menu up at the upper left! With no problem I could encrypt the new empty wallet so I stopped everything and brought back the regular wallet.
It is now synchronizing but I don't understand why it takes its time - after all all blocks are already here... and it says 19 active connections to bitcoin network!
we'll see