There could be several problems happening here. The most likely is that your player simply doesn’t like these burned dvds. Have you had success with burned disks in it before now?
Are you using -R (which seems to be what your wrote) or are you using +R disks? If you are using +R, it might be possible to increase compatibility by bitsetting the disks to make them look like a commercially made DVD-Rom (like a dvd movie you buy). We would have to know the make and model burner you have and which program you are using for the acutal burning to disk. It is easier to bitset with some drives than others.
Next, I recommend changing the type of disks you are using. Try some 16x Verbatim. -R might be best to start with.
Reduce the burning speed down to 12x on these or 8x. If you want to try again with your HP disks, definitely slow down the burning speed to 8x.
I’m not a fan of Winavi. There are free alternatives that are better. You should look into a program called FAVC. There are a couple of others that are free and worth investigating as well, called DVDFlick and AVStoDVD. FAVC can be set up to burn automatically with an excellent burning program called ImgBurn. ImgBurn is free to use as well.
If you use FAVC or AVStoDVD, use the HC encoder option. It will give you excellent results.