it's now my second attempt at upgrading from 15.10 to 16.04. This window is now open for 30 hours and it says 'running partial upgrade'. It seems to be active. Checked green are ' preparing the upgrade' and ' Getting new packages'. It seems to be still ' installing the upgrades'. Would it not be more economical to download the new version and run a fresh install? Anyhow this process reminds me of the dark ages of Microsoft windows using a stack of floppy disks! I will interrupt the process right now.