My DVD-ROM won't recognize DVD movies, but plays CD's perfectly well. I've downloaded 5 different players, to no avail.

Do it only if u r a professional..

open it up, with the lens assembly there is a small preset, turn it using a screw driver a little anti-clockwise..clean the lens with clean cotton using isopropyl alcohol..
if not done, replace the lens assembly..
or else, replace the drive with a standby n see..

i gotta know: is ur drive pata/sata and the device make n model..
assuming that ur drive is pata, n u r a professional n aware of bios/cmos setup utility handling..!!
open up ur system cabinet and see if all the data cables n jumper settings at the back of the drives (master/slave selection)..itz most important..!!
however, at the bootup (0.29sec) start pressing briskly the key to enter cmos utility or bios setup (eg. F1/F2/F10/Del as applicable)..glance in the standard settings if r detected individually..change the 'Mode' if m/b is hybrid type(both SATA+PATA) : Native/Compatible/Enhanced (as applicable)..
see if ur device needs any additional driver or not, if so try downloading..
also try checking itz data cable for loose or faulty..
above all explanation is applicable only if itz not being detected by the m/b or system..(not for reading or writing problem)..

contact ur system admin/vendor....