Unable to boot Ubuntu 14.04 from DVD after failed upgrade from 13.10

I had a working french 13.10 Ubuntu install working fine with NVidia graphic card.
Tried to upgrade to 14.04 and I had an error regarding a non ASCII char found in some file (Python exception).

Upgrade was interrupted and apparently half way in. Doing a dist-upgrade upgraded all the packages into 14.04.
After I rebooted, system is not operational. No unity, no possibility to start a shell with cntl-alt-t.
I had to use cntl-alt-1 to get a shell.

Didn't knew what to do. So I made a Ubuntu 14.04 DVD from the iso for a fresh install. Checked MD5sum and download was without errors.
Unfortunately it doesn't boot. It keeps booting from the disk even if I configure the bios to boot from the DVD.

Now I'm stuck with a hang office PC.

Is there a way to start NVIDIA driver and unity on my hang PC ?