Adding second 3tb+ drive not working

[nonuniform]

I've got an older Gigabyte z68 ud3 m/b. I've got 4 sata drives + sata dvd drive connected and working. One of the drives is a 3tb drive. Win7 64-bit sees the full capacity fine with the Gigabyte board.

I've got one extra sata port, so, figured I would add a 4tb drive. No dice. I can't see the 4tb drive unless I disconnect the 3tb drive. Can't seem to have both. When I disconnect the 3tb drive, Windows disk management sees the uninitialized 4tb drive just fine.

Thoughts? Clearly I'm doing something wrong.

 

[Elixer]

Odd.
Sounds like a BIOS issue of some kind?

 

[hhhd1]

Maybe there isn't enough power for all the drives.
This could be a problem if you are using power cables splitters.
Or if the Power supply is going bad.

 

[JimKiler]

Is the BIOS seeing all drives connected at the same time? Isolate if the mobo or Windows is the issue.