There are quite a few possibilities.
First question: Are these SATA drives (less-wide, thicker data cables with seven pins) or IDE drives (wider, very flat data cables with forty pins)? Only IDE has master / slave.
Second question: Was there data on that second drive before, and was it your boot drive?
The most likely possibilities are
1) Due to file protections keyed to the previous install, you don't have access rights to the root directory on the data drive.
2) The data drive was formatted during the install and has to be restored carefully. This is not likely if it shows space used.
3) The files on the data drive became hidden.
Does the data drive show up with a drive letter or not?
Can you show us the information in Disk Manager for that drive?
What do you see if you use Windows Explorer to see the root of that drive (assuming that there is a drive letter)?
In Windows Explorer, what properties are shown for the root directory? Especially protection?
Simplest case: the files are hidden and/or system. Make sure that you configure Windows Explorer in your new installation to show hidden and system files.
We will try to distinguish between the cases, based on further information. You will need to be logged into an account with admin privileges to do meaningful exploration.
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Sorry for the shotgun approach, but there are many possibilities and I can't distinguish among them without looking at the answers to some of these questions.
Did you have a backup?