I have seen this before... multiple possible causes.
It the recognition of your drives by the OS worked "once" and then not again, then I have seen this several times. Unhook each of the new drives one at a time to verify it isn't an actual hardware problem... meaning the board of one of the new drives.
Another condition that occurs AFTER recognition has to do with File Table memory... some are dynamically adjusted and this sometimes fails after a HDD format.
Example: I would mount and format a drive in Novell Netware and even put files on it, but try to reboot and it would fail to load the volume (partition section) on a given drive because of memory allocation issues.
This was caused by the loading order of Memory Management (relative to partitions/volumes) and disk drivers etc.
What happens if you just unhook both new drives completely?
Don't do anything extreme yet though, it is most likely just a driver/memory issue that can be sorted.
So... are the drives formatted yet? And if so, what are the partition sizes? I do not know all the size barrier issues with drives that large, but there has always been them in the past.
Let us know what you find out. Good luck.

MrBlackCat