Partitioning – MBR vs GPT for 2TB External Drive Initialization

Use clonezilla to make an image of your hdd then restore that image to your new drive and it would be as if nothing happened. http://clonezilla.org/
You'll have to boot clonezilla from a USB or CD in order to do this.

Alright given the new information I recommend you do the following:

1. Partition your 3TB drive in half.
2. Create the image using the software above while saving the image to the second half of the partition you just made. (Clonezilla will let you specify where you want to put the image)
3. Restore the image to the first half.
4. Once it seems everything is good, format the second partition then delete the second partition
5. Extend the first partition to cover the entire drive.

Note: If you don't have enough space then you might have to remove some of your games then just install them after the image goes down.

I recommend just messing around with it till you get what you want, because as long as you have the original you'll be fine.

It looks like something has trashed your GPT data -- both the main data structures and the backup data structures. I don't know specifically what might have done this, but a buggy partitioning tool seems like the most likely culprit. Another possibility is that there's been some confusion over something like a RAID configuration -- if the disk was originally prepared with your motherboard's RAID features active and then accessed with the RAID features inactive, something like this might have happened.

Two options seem most reasonable at this point:

1. Re-create your partition "blind." The vast majority of modern partitioning tools begin partitions at sector 2048, so you could use gdisk to create a partition that begins at that point and that ends at the last possible sector. This stands a good chance of succeeding, but there's a risk that if your original partition did not start at sector 2048, you could end up damaging it when you try to access the new partition. Also, some tools will try to create a new filesystem when you create a new partition, so using them would be risky at best. (I recommended gdisk for this task because it does not touch the partitions' contents, just the partition table that defines them.) Also, if the disk held an EFI System Partition in addition to the main data partition, the main data partition would not begin at sector 2048.
2. Use a tool like TestDisk (included on many Linux emergency systems, such as PartedMagic and System Rescue CD) to search for your missing partition. (There are Windows equivalents to TestDisk, but I don't know what they are, offhand. You could do a Web search to find them, if you prefer to work from Windows rather than boot a Linux emergency disc.) This will be more likely to find your partition if it was placed strangely, but tools like this can become confused if the disk has been re-partitioned in the past -- they can sometimes detect the remnants of deleted partitions and try to re-create them even though they're no longer valid.

Take your pick as to the approach, and good luck! Whatever you do, though, be cautious. You might consider doing a raw disk backup to a spare disk, if you've got one that's big enough to hold all your data. If you do this, though, be very careful in specifying the source and destination disks, or your backup could end up trashing the data you intend to save!