So this Matshita UJ-850S is your DVD-RAM drive?
Have you made sure you have the latest drivers from Toshiba's website?
Have you made sure the disc you're trying to read is clean?
Have you made sure that the DVD-RAM drive's SATA data+power cables are securely connected?
Bear in mind that DVD-RAM drives have issues reading some types of DVDs, so it may be an issue with the type you're trying to use.