In that case I think maybe the sensible thing would be to disable RAID temporarily and use AHCI mode until you figure out which drive has failed and why. If your OS is on the RAID volume then you will need a bootable diagnostic disk of course. Most HDD manufacturers have them available for d/l and they normally work with any drive and can access SMART data. It won't mess up your OS install since it will be available once again when you go back to RAID mode. You may even be able to tell which drive is the problem from the BIOS alone. I think you are looking at a Windows re-install in any case though, but better to find the problem first, replace the drive if neccessary and rebuild the array before doing this.
PS I don't know of any Windows based tools which are able to report detailed SMART attributes of individual drives within an array, but worth checking if perhaps the Intel Matrix console, or similar software can provide some more clues as to what has gone wrong.
