I left the pc to defrag with a free trail program called PerfectDisk 10 over night and when I woke 8 hours later and restarted the computer the screen that displays the information about the hard drives, one of the 2 250g in raid0 mode says "error occurred".
I was able to get into windows vista and it work but I just like to know why it says that and what
could to wrong
It's possible the program you used caused some corruption. Luckily it didn't bring down your entire array, apparently. Do you remember the entirety of the error message?
its not really a message, its when the pc first restarts and has not started windows yet and all the system hardware info is displayed and there was a list of the hard drives and their status one of the 2 250g hdd say "error occurred" under its status in orange and the other is normal ( can't remember what it said) which was written in green. the raid 0 status is normal as well