[blue68f100]

You need the Guardian OS which normally resides on the HD's. If you have the original HD. Install them in the order they were removed, Snapshots and AV should be disabled. Then install your new HD in slot 2, boot the 4500. After about 5-6 min you should see activity on the new HD as the OS is transfered. Then power down and remove the old HD and move the one in slot 2 to slot 1. See if the unit boots if so hot swap the remaining HD.