I need to knw a few things b4 i can advice u sumthing:
1.) Wich DVD WRiter u are using?
2.) Make sure wichever DVD WRiter u are using, the lens is clean from inside, u can buy a DVD Lens cleaner from the market for Rs.100/- or so..
3.) Wich type of Media are u trying to burn (DVD 4 GB or DVD 8GB) and hv u tried burning different media brands (Like cheap ones as well as trusted ones like Moser baer')
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In any case, jus clean the lens of the DVD with a lens cleaner and see wat happens..

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Cheers n e-peace...