I have a ThinkPad X130e. I installed Ubuntu 12.04 LTS amd64 on it. All worked fine until yesterday. While diagnosing another issue I reset the BIOS / UEFI to defaults. Afterwards Ubuntu did not boot any more. The ThinkPad shows Operating System not found and that's it.

Did the BIOS / UEFI reset somehow nuke GRUB? If so how is that possible? How do I fix it?