Get into BIOS setup and see if it shows there. If the BIOS doesn't see it, Windows won't either. The other thing is I have to ask if you've created a partition and formatted the drive. You have to do that before it will be assigned a drive letter.
I have a Dell Inspireon(sp) and want to add a SATA drive. I have installed the drive, but the computer does not "see" it. What to do?