Well the PSU is modular and there is a big chance that he connected the SATA power cable to the wrong socket on the PSU, so he damaged the disk. But in such case it wouldn't be detected on Disk Management... That's weird... I also told him to replace the SATA data cable just in case, he told me he did. He is a novice, so I don't completely trust him. I'm sure it is something simple, but I cannot visit him during the week, so he has to go to the store Service and pay...