Laptop optical drives have become quite standardized over the past four years... Usually, you must remove some of the guides on the old one with a screw driver, and install them on new drive.
We buy ours so as to fit a number of model, with only those guide adjustments, in lots of 24 to a case...
Most online stores, such as Directron.com, Frys.com, CDW.com, NewEgg.com and perhaps 100 others will tell you if something is going to fit or not...
We have had our best luck with Teac, LG, and Samsung, and our poorest luck with Sony, Sony Nec, HLD, HLDS...
First thing to do, it seems to me, is to take out the old one... If you cannot do that, you probably don't have the system figgered out well enough to put in a new one.
It has been a long time since I have seen a drive that didn't fit after changing the guides and snaps around with a #0 philips screw driver.
When you remove the old one, you can see on the label on the bottom what are the specs, and current model.
When you install a new one, be extremely careful not to get oil, dust, or fingerprints on the lense of the optical drive. Other than that, just make sure it connects properly so it does not come shooting all the way out of the machine.