SATA ports 3 & 4 will not see any drive on my Dell optiplex 745

When I install a second hard drive on the Dell Optiplex 745 in either sata port 3 or 4, it is not reconized by the computer? These ports show up in bios but are not active? How do I turn on these ports for use.

PS: bios level is 2.1 12/14/06

Thank you.