i have a dell dimension e310 with a HL-DT-ST DVD+-RW GSA-H21N drive and it will not recognize dvd's. Any help on this problem.
There is a possibility that your DVD laser is not working. But I would first try updating the firmware, download and installation instructions here.
There is a way to test the drive's ability to read DVDs by running this diagnostic program for a bootable flash drive. There are many procedures for making a bootable flash drive such as these.