I finally found a working solution to the problem : I disabled the "legacy USB keyboard" option in my BIOS.
It is still not clear to me why this option should prevent the use of a PS/2 keyboard. -- PS/2 keyboard does not work https://launchpad.net/bugs/48877 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
