WMP, of course, cannot play DVDs without the codec. Your ASUS DVD player may be an older version of WinDVD which is not compatible with WMP10. The reason WMP is not a stand alone DVD player is that the codec needed requires a licensing fee. MS is not going to pay that to run a free media player and users must do so. I would suggest uninstalling and reinstalling your ASUS player. This might be a case similar to losing plugins when updating a browser and needing to reinstall them. If this does not fix it, my guess is the codec is not going to work with WMP any longer.