Is power connected to the hard drive? If so, you may consider using a power supply tester to ensure your power supply is functioning properly.
Here is a page stating that they are selling a 2 tb hdd pulled from a working Dell 760. Therefore, it must be possible to use a 2 tb drive in that model.
This is a genuine OEM Dell Optiplex 760 7200RPM hard drive. This hard drive was pulled from a working Dell Optiplex 760 computer and is guaranteed to work with all Dell Optiplex 760 computers.
Optiplex 760 and 3TB Hard Disk Windows 7
Beyond 2TB
Using a hard drive larger than 2.1TB on Windows-based computer systems may require special setup considerations