I RECENTLY had two sata western digital raptor 150 gb hard drives set up in a raid stripe configuration.  They were running windows XP and everything WORKED fine. I then purchased a WD sata Velociraptor 300 gb,  installed it  and disconnected the other two hard drives.  I installed vista 64 on this new hard drive and had no real problems with it.  I then decided to give one of the 150 gb drives to a friend and use the other one to run xp on my computer. The problem occured when I reconnected the 150gb drive again. The POWER was off and I think I had the computer unplugged.
when I started loading xp it said there was no hard drive to load into. I then restarted the computer and went to the bios.  It showed both of my sata dvd burners but no hard drives and I even tried auto detect to no avail.  These hard drives have almost no hours on them and one of them is $300.  Also RAID is turned off in my BIOS.  My motherboard is a bfg 680i, 750 watt thermaltake power supply,  Two BFG 8800GTX OC2 video cards in SLI,  4gb of 1066 Mushkin Ram,  two Samsung SH-S183L DVD burners,  and an Intel QX6700 CPU if that helps.

            Can someone please HELP me
            Thank you
             Dennis