HDD to HDD data transfer and then everything gone

I use a WD Green 3 TB hdd (internal) as a secondary hdd. It's not the boot hdd. I run windows 8 64 bit on a separate hdd. Today I took my 3TB hdd to my friends house. He runs win 7 64 bit. I connected my hdd to his pc and copied some data from his hdd to my hdd. But when I connect my hdd to my pc, all the copied data is gone. There is no sign of the data. I tried to run chkdsk but some sort of error came and the disk became inaccessible. I restarted the pc. Now I see some data but not all (All of my previous data is there and part of newly copied data). I just ran a chkdsk in cmd with /x /f /r and it's running and it'll be taking a while. What's my problem ? This 3 tb is about one week old.

 

Did the Windows 7 computer have a UEFI BIOS, or have a SATA controller compatible with drives over 2.19 TB as well as designed to recognize 4KB blocks?

Was the HD connected or disconnected improperly, (ex., while the computer was running).

Was the computer shut off w before the data transfer had completed.

It could also be due to ESD (electrostatic discharge) and/or rough handling.

 

I am not sure if that pc had UEFI BIOS and whether it had sata controller compatible with drives over 2.19 TB. My HDD was GPT partitioned and that pc did support my HDD.
No, the HDD was not connected or disconnected improperly. And, no the pc was not shut off before data transfer.
I am not sure what a ESD is. But about rough handling.. I did walk about a km with that HDD in my hand and it was obviously in some swing. Can it be possible for the data loss ? I did get some of the copied data. I copied over 200 GB. A few files that I copied at first, are there.