I've been going almost solid through troubleshooting for 3 days with this external HDD.

The first was 'lost at sea', quite literally it fell off a boat. Don't ask.
This backup drive was Transported an hour and a half by plane, securely wrapped in hold luggage. When I tried to re-assemble my PC at the other end, this backup drive wouldn't run.
It's a 1T WD External. I was it's first owner and I have never partitioned it myself. It does have what I believe to be a hidden file (not sure) that 'mounts' every time the drive starts up, which windows sees as a CD and I'm unsure if this counts as a separate partition. It's an instruction to 'Caring for your drive', I think. But other than this, the drive is just one whole section/single partition of files and photographs, with no OS.
At first I thought it was a power issue as it just wouldn't start up.
But after testing for that failed I decided to sata wire it into my motherboard.
It wasn't detected by windows 7 so I ran 'Disk Management' which found it but couldn't do anything with it, let alone assign it a letter. It kept wanting to initialise it, Which I declined.
After a few random programs scanned it and found nothing, I Ran the 32bit TestDisk on it.
I assumed it was an Intel Partition, but frankly I'm unsure.
TestDisk found something and told me the drives "partition sector doesn't have the endmark 0xAA55" whatever that means.
I continued with both a quick search (Around 1h Hour) and after that a deep scan (7+ hours, I fell asleep), both of which told me the same thing about 11% into the scan:
Disk /dev/sdb - 1000GB / 931 GiB - CHS 121601 255 63
Analyse cylinder X/121600: X%
check_FAT: can't read FAT boot sector
Invalid FAT boot sector
0 D FAT12 210454 186 18 368100 78 28 2532576197
FAT12 210454 186 18 368100 78 28 2532576197
The QuickScan and the DeepScan both then say this at the end:
Disk /dev/sdb - 1000GB / 931 GiB - CHS 121601 255 63
The harddisk <1000 GB / 931 GiB> seems too small! << 3027 GB / 2819 GiB>
Check the harddisk size: HD jumpers settings, BIOS detection...
The following partition can't be recovered:
Partition, Start, End, Size in sectors
> FAT12 210454 186 18 368100 78 28 2532576197
[Continue]
1296 / 1207 GiB
I've run to scans twice each now with the same results. Continuing leads to TestDisk showing no partitions in the list and asking if I would like to "add a partition, load a backup or continue".
Continuing further then leads to TestDisk telling me there is "No partition found or selected for recovery"
It then gives me the option to quit.
It seems to recognise something is there but will not allow me to go any further.
This drive contained 10 years of data, any help you can give me would be greatly appreciated, I'm almost out of ideas.