Here's a possibility to check IF you are using Windows XP. This idea does NOT apply if you are using Vista or Win 7 or 8.
Windows XP never had a "built-in" driver for SATA devices - only for PATA (IDE) devices. Normally, this means that XP would need the proper driver added so it can use a SATA device. But there is a work-around in most mobos to allow you to avoid this, if you wish. We'll get to that.
So, only IF you are using Win XP (or a previous Windows), the "normal" way to solve this problem is to install a device driver for the SATA drive (or it may be referred to as an AHCI device, which is really what a SATA drive is). This process would allow you to use the drive as a true AHCI device for data storage and retrieval, but NOT allow you to boot from it. I think that is what you are trying to do. You need the SATA (or AHCI) device driver for your mobo for this, and usually it is on the CD (or DVD) disk that came with your system or mobo. Look in the manual, and on that optical disk, for a utility that will install such a driver in your Win XP (or whichever version) Operating System, and follow the instructions. Do NOT worry about the complicated procedure for putting the driver on a floppy disk and installing it using the "F6" key during the first installation of Win XP. That is ONLY if you need to make this SATA disk a boot disk. Look for the way to install the driver ONLY on an already-install Win XP so that the new SATA drive can be used for data storage and retrieval.
Once this i s done, your Win XP will boot as usual from your current older boot drive and load (also from there) the driver needed to access the SATA drive. Then you can use it. But since it must load the OS first, and then the driver, it cannot BOOT from that new drive. A different process is needed if you wish to boot from it, but I understand that it not your need.
Now, the "work-around" I mentioned. Because this was a problem for many users when SATA drives were introduced at almost the same time as Win XP, most mobo manufacturers added a trick to the BIOS they use. This trick allows Win XP to use the SATA drive without having any extra driver software installed. In the BIOS Setup screens where you configure the SATA ports, there is usually a line for SATA Port Mode, and the options you can choose are things like "IDE (PATA) Emulation", "Native SATA", "AHCI", and RAID". Normally you only use RAID if you actually are trying to set up a RAID array, and you do NOT appear to want to do that. Setting the port to AHCI or Native SATA makes the drive work the way it should, but does require installation of the driver in Win XP. But if you set this to "IDE (or PATA) Emulation" mode, the BIOS intervenes and makes the actual SATA drive appear to Win XP to be a plain old IDE drive that it can use easily, and it all just works with no driver added. The downside of this is that you lose a few small enhancements that true SATA drives offer, but many users never need those features anyway.
Now, some BIOS's allow you to set this option independently for each SATA port. If that is your situation, check how that option is set already on the first SATA port that already has a working SATA old drive. Whatever that setting is, you should make the second SATA port mode the same. Other BIOS's make the choice apply to ALL of the SATA ports; if yours works this way, do NOT change it - it already is working for your other SATA ports, and you don't want to change them.
As I said, all this ONLY applies if you are using Win XP (or a previous Windows). VISTA and Win 7 and 8 "fixed" this issue by adding "built-in" drivers for AHCI devices, just as previous Windows has such tools for using IDE devices. If you are using Win XP, it is possible on some mobos to have some SATA ports (the two with your old drives) configured to IDE Emulation, but the other ports left by default to AHCI. If that is your system, Win XP cannot figure out the new drive on a AHCI-cofigured port, and you can change the configuration.