Humax-burned DVDs wont play on my PC

Hi all- brand new to the boards (and new to TiVo too)....

I have burned several DVDs with my new Humax DRT800, and have tried
playing those DVDs in various devices. The DVDs play successfully in
one PC but not in another (they play in regular DVD players too).

For what it's worth, the PC that doesnt play the DVDs from Humax DOES
play regular old store bought DVDs (The Matrix, Unforgiven, etc.).

I checked the specs of the drive itself- its an NEC DV-5700A and it is
supposed to accept DVD-R media, which is the format the Humax uses.
However, I cant even get the PC to recognize that there is a disc in
the tray- it hangs the PC whenever I try one of these Humax-burned
DVDs.

Can anyone shed some light on this problem? I really dont want to have
to wait until TiVoToGo to get a Tivo-to-PC connection.

Thanks!