Normally an Ext HD of this size (never seen different!) will be primarily mains powered, the USB controlling just the data side of things.
I think that now is a good time to hook up the external to another PC and begin the process of elimination. If it works there and your music plays, then it is looking very much like the PC itself, wouldn't you agree? Thing here, is to remove any doubt about the HD before delving further into the PC.
Nearly all externals are ready formatted in FAT32 so that any other PC can read and write to them. Very unlikely that you have the better, but NT & XP only NTFS file system in place.
Let us know how it goes,
Conan