Rebuilding mirrored raid array

I have a motherboard with an nvidia 560 chipset. I've used it to create a mirrored array of 2 drives, but one of them was unplugged while windows was running. This messed up the raid array, and now 2 partitions are visible to windows instead of one. When i go to the raid utility (f10 before windows boots), it offers me the option to "press R to rebuild array" on either of the hard drives, but when i do this, it goes back to the raid utility screen. Do i have to wipe one of the drives first before I can rebuild the array? both drives are intact/are not corrupted.