Based on your description and the image information it seems the HDD could have failed. As much as we can do at this point is trying to disconnect the HDD and reconnected back in.
If the HDD is still not recognized, you should contact HP for them to help you with the special raid configuration you computer may need or for them to help you saving the information.
That's what I feared. Unfortunately disconnecting and reconnecting the HDD did not improve the matter. Looks like it's time to contact HP.