XP can't read DVD but Media Player can

I have XP, SATA HP DVD- RW as D:\. Put a commercial DVD or CD with MP3 songs
in the drive and using My Computer, double clicking on D:\ gives blank
directory. When I open Media Player, I get songs on D:\ and clicking on any
song successfully plays it. Media Player also plays the commercial DVD.

Somehow the DVD reading routine used by My Computer is defective, but Media
Player must use different code and it works. Physically the drive must be OK
or Media Player won't work either.

Has anyone even heard of this problem before?

Any suggestions? Thanks in advance.