My 2TB Seagate USB HDD used to work perfectly fine on my PS3 (Used through IrisMan), but now, after I added 15 PS3 games and 4 PC games, it doesn't show up anywhere on IrisMan, MultiMan, or WebMan Mod when I refresh my games list. It has always been NTFS MBR (Formatted with Rufus), and I never reformatted it after I confirmed that it worked the first time. I have tried using PrepISO (Holding X and not), and I still cannot get it to work. If anyone could help me it would be greatly appreciated! 
Saturday dude. 
JM 