Thomas. Andrews, it is very important to know which type of RAID did you set up? RAID 0, RAID 1 or RAID5?
Please access the onboard RAID BIOS and check the status of the RAID. If it is degraded you should be able to replace the defective hard drive and rebuild it. There is a 50/50 chance the RAID could be rebuilt without problems.
If the RAID status is failed, that means that the structure was corrupted since the beginning.
Which Operating System are you using? Where you installed it?