first, check in the bios to make sure it's being detected there. if it is, then check the type of connection... if the main drive is in IDE mode the 2nd drive should be in IDE as well (generally windows won't detect AHCI mode unless windows is installed when the main drive is in AHCI mode)... if the drive isn't in the bios, then it's either dead or not plugged in right. make sure the power cord and sata cables are plugged in correctly, try another SATA cable if you have to.
once its detected in the bios it will be a simple procedure to get windows to recognize it.
go into disk management, click on the unassigned drive, format it, you're done. Windows will automatically assign a drive letter once it's formatted.