It's either. In my L1020, it was a hardware failure that caused the missing bootable option - for this only a replacement of the board would fix the issue. On the other hand, a corrupted software data can also lead to the same error but it should be easily fixed either by yourself or a service center.
You may refer to this Microsoft FAQ page for a detailed step-by-step procedure on how to go about with the Lumia Software Recovery Tool.
If the LSRT method didn't work, you may need to bring your phone to a service center already.