First off, what OS are you using? Then if you installed this new drive, is it SATA or IDE? If IDE, did you check the jumper for the correct setting? Look at the old one for a reference as to match it, if possible. Also, check the BIOS page to see what is actually detected at boot up.
i just took the cd-rom out of my gateway and installed an iomegazip cd burner, but both my cd burner and dvd-rom are appearing as a D: drive. they both work but now the dvd-rom won't read any type of disk but my cd burner works just fine. why are they both appearing as a D: drive?