I'm assuming this is your TV?
The manual says:
Media Play only supports USB Mass Storage Class (MSC) devices. MSC is a Mass Storage Class Bulk-Only Transport device. Examples of MSC are Thumb drives, Flash Card Readers and USB HDD (USB HUB are not supported).
A USB device that requires high power (more than 500mA or 5V) may not be supported.
If an over-power warning message is displayed while you are connecting or using a USB device, the device may not be recognized or may malfunction.
If a USB extension cable is used, the USB device may not be recognized or the files on the device may not be read.
Does any of this apply?
Also is your 2Tb HDD a desktop or a laptop one? If its a laptop one I suspect the USB port on the TV may not be able to provide enough power since they take (slightly) more power than a 500Gb would. USB ports on TVs aren't particularly fantastic at the best of times.