open ur hard drive in hexeditor (HxD), press ctrl & g enter Offset: 80000 and Replace the Data With: 58 54 41 46 00 00 00 00 00 00 00 10 00 00 00 01
use Xplorer360_09b6_250gb.exe when done! hope this helps!
Will this also work on a 60GB genuine HDD? Reason I ask is that I just overwrote my genuine 60GB drive with Acronis (that's what happens when you are too busy talking on the phone!), MBR and all, and now I am having the same issue with this drive! I reformatted it on my xbox but xport, nor xplorer detect it.
I tried editing the hex of the 60GB drive to the value you mentioned, but can't detect it in the 250GB, 120GB and standard(?) versions of Xplorer360
Tonight is not my nigh

UPDATE:
I actually made a back up of the first 16 sectors of the 60GB HDD in Xport before I killed it. I open that up in HxD then copied all that data over to the HDD and now it works.
I will try the 100GB tomorrow in HxD. Will that drive not work either since it doesn't have the hddss.bin file flashed to it?