Adding a second hard drive

Im trying to install a second hard drive. The problem Im having is that the new hard drive is being recognized as my primary hard drive.I need to change it to the secondary in the bios setup. Can somone help me? Also if i disconnect the original hard drive and just load my system off the new drive, I am able to read the drive fine. and if i disconnect the new one.and read off the old one it works. but if they are both connected i get an erro that says disk E: is not ready. then i get the abort retry fail menu in msdos.
thanks for anyone that can help.