I was formatting my drive with Windows 10 installer. I deleted the existing partitions fine, and I was left with one giant 2700gb partition.
When I went to format this, it said it failed to create a partition and then left me with two Unallocated Spaces, one 2TB and the other with the remainder.
I've downloaded Partition Wizard and deleted all partitions on the drive, but they still show up separate and can't be combined.
Here is a screenshot http://i.imgur.com/9wmCZDT.png