bios can’t detect my hard drive

every time i restart my computer, i must enter setup to change the bios to “user defined”, otherwise the bios will say, “not installed” concerning my primary master hard drive. why is it doing this? I just bought this computer and added nic card anddsl modem and more ram. WHY is the bios not recognizing my hard drive unless I set it to user defined? i have to set it to user defined EVERYTIME I restart the computer!