You don't say what errors if any you are getting ?
have you formatted the disks before trying to write ?
What DVD drive is it ?
I have just got a new Sony DRU-18 DVD drive. It wont record on Memeorex DVD's or Bulqpak but does work ok on Sony ( of course !) but they are expensive. It also works fine on Datawrite media +R & -R.
Might be worth buying 1 or 2 of different makers media just to eliminate that.
Apart from that my brand new machine needed a firmware upgrade before it would record DVD's so check you have latest drivers installed by checking drive manufacturer's web site.
All pretty general stuff I'm afraid but hopefully someone else may post a more specific responce.