it's difficult to know what to suggest;
sata controller on the Humax could be faulty, new hard drive could be faulty, drawing ~5W of power could be causing power supply problems.
You haven't mentioned what casued the original 320GB drive to be replaced; anyway, I think the next step would be to put the new hard drive in a PC, do a full format, not quick on it, make really sure that you select the correct drive, from 1TB expect to see ~960GB +/- 5% available once formatted, and then run the disk error checking on it.
With the drive still in the PC, run another test/verify against it, there's a really simple program:
http://www.softpedia.com/get/System/System-Miscellaneous/H2testw.shtml
this will write to the drive and read/verify it back - I've not used this for drives, mainly for usb sticks, SD cards etc, but I'd be wanting to check this in your situation.
Windows will overwrite the entire hard drive, it's entirely possible that you'll find no problems with the drive on the PC, put it back into the Humax, reformat and everything works, I'd advise a factory reset and another reformat if this is the case.
If the PC has problems with the drive then you have the answer, it's either back to ebuyer with it and/or you could run the WD data lifegaurd for windows diagnostic against it to be doubly sure, should be around this link somewhere:
http://wdc.custhelp.com/app/answers/detail/search/1/a_id/1211/c/130/p/227,294
Obvisouly with any disk checking tool be very careful that you select the correct disk, it will wipe you main windows disk if you tell it to.
If your PC finds no problems and Humax still struggles and the WD diagnostic hasn't found anything then let us know. Other members have had problems with this drive, but managed to overcome them
