The player may be a little bit picky and you might have some problems with your original disks if new copies work now in the player.
What type of disks are you using? Not just the brand, and if it is + or -, but the id code. Run DVDIdentifier or Nero CD/DVD Speed to get the mid code.
The disks most recommended around here are Verbatim 16x and Taiyo Yuden 8x +R.