Wd 160 caviar blue issues

hi, I bought last July 60 hd wd caviar blue 160Gb to make as many PC (same hardware configuration of others made in the past). Now a month after the PC started to give bsdo the bios sometimes does not reveal the hd but sometimes it shows the disk is corrupted or in other cases the system starts, but disk access is so slow as to render it unusable. Using the WD tool for testing some are totally not working and after a low-level format can reuse the disc for a few weeks but then the problem returns. any ideas? Keep in mind that on 60 discs now will be spoiled about 30
Thank you in advance for any advice

Extra note

all motherboard ar asrock g31m-gs

all cpu are intell core duo

all have a micro atx power 400W

all video driver is a asus en210 silent

all pc have only 1 hd and no other driver

maybe some problem with the power?

are you sure its only the drives fault??

30 drives is very much O.O

the pc are in two different room (inside the same building) and every room have 4 different power line,

in the same building i have around 40 more pc and noone have this kind of problem.

i can’t find the proplem