My primary SATA hard drive on my Dimension 8400 has my XP operating system on it.  My secondary SATA hard drive (storage, & some programs) developed a problem, so I replaced it with a new SATA drive.  The "Device Manager" sees the new drive and says it is operating properly, but when I open "My Computer", the new secondary drive is not there.  I did "Dell Diagnostics", and the new drive is recognized, and "Dell Diagnostics" found no problems.  I have been into "Setup", and the new drive is also recognized there.  ?????, any ideas?