Comment 5 for bug 494654

Is likely as Andy suggested. There is also a BIOS bug present (_GTF (get task file) returns an integer and not a buffer), but that might just be coincidence. Tobias, please let us know whether the rootdelay helps. Alternatively when you get dropped into the shell check with dmesg, whether sda is present (or look for the /dev/sda7 entry). If that shows up, say exit and the boot should go on.
With a successful boot, also add the dmesg of that to this bug.