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If your DVD recorder is only new or a few months old and you did not play many discs in it since you first got it (such as under 50), then there is a good chance that it is a hardware fault which will need to be serviced. In this case, you will need to bring it back to the store for repair (which should be covered by the warranty).
On the other hand, if your DVD recorder is over a year old or you regularly use it for recording content, then it has likely built up dust on its lens. To clean this, you will need to use a laser lens cleaning CD (works in DVD players also). See this thread for more details on getting and using one of these discs.