The DVD-VCR unit won't accept any DVD - blank or

You may have a dirty lens on the DVD read head. There are CD/DVD cleaning kits available at some drug stores and electronic stores. Do not get a "CD cleaning kit" (that only cleans the discs), get a "CD/DVD lens cleaning kit" (it will have a special CD and cleaning solution) for $10 to $20.
If that's not it the DVD illumination LED may be dead. If it still plays CDs, but won't play DVDs, that's the problem. There are separate LEDs for playing CDs and DVDs.
Either way, if the cleaning doesn't work, it has to be fixed in an electronics shop.