raid not showing after boot

On a newly finished gamer, I have two drives set up as raid 0. I tried adding an external usb harddrive and when I rebooted, the raid drive (E) had been replaced by the external drive with no sign of the raid. After playing with the several things and rebooting, the raid was back and the external (F) also was there. Booting again later the raid was missing again!? This is on a MST P6N Diamond MB with two raid drives, a data drive and a DVD drive. Another problem that occurs once in a while is the boot sequence changes in the bios. I've hesitated loading any games to try the system out because of these concerns. I'm using XP Pro OS.Any thoughts?:confused

 

Are you using identical HDDS for your RAID?