Indeed, more information would be useful. However, my first guess is that during the installation of the CD burner (which, at this point, I am assuming to be internal), the connection between the hard drive and the laptop was severed & not restored. Usually, the entire case of a laptop needs to opened/removed for an optical drive to be replaced, and laptop internal components (especially screws) can be hard to keep track of. Check the hard drive cable to make sure it is still firmly attached on both ends. Also, check your laptop's BIOS settings, especially if they were fiddled with in an attempt to get the burner recognized (note, that if your laptop already had an optical drive, no changes should have been necessary to the BIOS).


-Matt
Quick PC Repair (serving the San Diego, CA area)
www.quickpcrepair.com