The problem is probably quite simple. You must make one of the dries the master and the other one the slave. You do this by removing the drive and looking next to the plug where your cable goes. You will see a small area that has 8 pins - 4 rows of 2 each. Look on the drive and it will usually show you the position of the little jumper to set the drive as master, slave or cable select. If you don't see the description on the label side of the drive look closely right under the little pins - you may see letters (M) for master (S) for slave and (C) or (CS) for cable select. Just carefully remove the little jumper and place it in the correct position. When you restart the computer it will recognize both. Hope this helps.
Bruce
June 2008