DVD writer will not play or record properly.

Problem something has rendered my DVDRW drive useless & it will not play DVD movies or play CD's. Also will not record or copy from the DVD or CD to the hard drive or from hard drive to DVDRW. There is no error message & does not operate with any DVD player software or with MS Media player.Tried to clean all cookies, cashe & registry errors & still nothing. My RAM has been replaced because of this & still did not correct. Thought that due to faulty RAM that memory issues were the blame.
Have had 1GB of RAM & now at 894MB with 104 MB unaccounted for.What is causing the DVD drive to play, freeze of stop altogether? Is it a buffer overrun issue or virtual memory? I have picked up info here & there but does not solve my problem. This issue has frustrated me for a month or so & have not the patience to continue anymore with it. Window XP has the most useless help or support information & wthout an actual error message or code, what can I do? Would appreciate any insight or solution to my problem. Thanks in advance to all who help.