A day ago, the drive would fail to copy certain files and had thought that this was a problem of the OS; later however, the system would only recognize the drive at certain times and so had to constantly unplug and plug the drive back in for the OS to recognize it. However, later on, the OS would fail to load the drive, and would even lockup until I disconnected the drive. Now, I've just tried removing the enclosure and connecting the drive internally, and although recognized by the BIOS, the system won't load the OS if the drive is connected (otherwise, if connected via its enclosure, Windows will detect that a USB device has been connected but won't load the drive and locks up -- it also displays a "Drive F needs to be formatted" with format/cancel parameters).
So, my question is... what do I do? This drive has over 1TB of useful data that I can't lose. Do I send off the PCB for replacement, run Spinrite or do something else which I'm unaware of which could resolve the issue?
Also, a similar problem to this has happened before with the drive (but was resolved after reconnecting the power cable) where the OS would return a "drive F needs to be formatted" prompt.
Any help is greatly appreciated!