With respect, when you are using a disc editor, you need to understand what you are doing. You also need an undo strategy. Hopefully DMDE did not touch the partition table.
Having said that, the original problem sounds very much like a Gigabyte BIOS bug.
After you have restored the full native capacity of your drive, you may need to rebuild the partition table. DMDE should do it for you, but if it were my drive I would do it by hand.