|uh... I just found out that the power cable for the hard drive just BUSTED. It's loose, and bent and whatsoever. So I changed to another cable, and it worked again.|
Also, the system drive was a Slave, whilst the second drive (the problematic one) is the master. Although there are not much problems from these (I think), but I still changed the system drive to Master, and the other to Master on another channel. Thanks OtheHill for the jumper tip.
So, the problem is (temporarily) solved. For any other guy facing the same problem, also check your power cable to see if it's busted or not.