This can happen with laptop drives. Usually, they are underrated in speed when compared to desktop versions. if u put a disc which is written on a high speed drive than ur drive, it wont recognize. this problem arises only on written dvd's.
otherwise, use a lens cleaner. Then, sometimes, some drives refuse to read certain discs. and others will read them perfectly.there is not much u can do with it.
Also, if it is an audio/video disc, pls check for the region.
This happens with my lappy sometimes, but those discs can be read perfectly in my desktop.
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Rajeev V Nair
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