faulty HDD, Back up now!
I had 2 x WD 500 Blue a few yrs ago. very slow R/W ~3MB/s
the lifegard tool said read head error after failed to boot.
then I formatted it and change SATA cable and ports, still the same speed. so now I just put it in my HTPC just to see when it will die.
TW forum also had similar case.
that is why I won't buy blue again.