I'm with the OP on this one: hook it up to an available SATA port as an internal drive. That way you should be able to isolate whether it's the drive or all the interfaces that have the issue. If you had only used the Belkin, I'd be immediately suspicious of it (not a big fan of Belkin's gear here), but you also tried some others and they didn't seem to work. I'm wondering if maybe it's a BIOS issue? (Seems kinda high and outside if your motherboard is at all recent, though.)
This link: http://wdc.custhelp.com/app/answers/detail/search/1/a_id/1679#
may help you find out more about your drive. It covers the entire family of Caviar Green drives from 1 to 3.5 TB, so sift the data wisely...
At the minimum, it will cover jumper settings and so forth to get it working as an internal.
This drive is rated by WD to work with Linux. You should not have too many problem seeing it unless your motherboard BIOS won't support it. Even then, via a USB interface it should still be visible and usable if that interface complies with standards.
How do you have your drive formatted? The Belkin site for the N300 says it only supports NTFS and FAT32...
For compatibility with any Windows systems on your router, that might be a good idea anyway. (Of course, the other interfaces you used might support other filesystems, so this might be another red herring.)
The important thing is to determine whether or not the drive is functional in its designed environment - before your warranty or return options run out!