Sometimes the new drive has a different configuration then the old drive. 
Some laptops require a drive that works in cable select mode (CSEL) - the 
laptop determines with drive is a slave and witch is a master by its 
position on IDE channel. Some laptops require a drive that works in 
master/slave mode - the drive is set as a master or as a slave through the 
firmware flash. If the optical drive is not configured properly, you'll get 
an IDE ERROR on startup. Sometimes you can find the information about 
optical drive configuration on the top of the drive. It would be CSEL for 
cable select and M/S for master/slave.

http://www.asklaptopfreak.com/laptop-notebook-help/category/replace-cddvd-drive/