My computer suddenly have no sound (onboard sound card)for the Right Front.
And I have added a new PCI sound card, and no sound for the right front as well.
Is it mean there is something wrong with the M/B?
It sounds far more like the right front speaker quit. The output from an expansion card is totally separate from onboard sound. You could easily have a broken wire inside the speaker cord from tugging and moving it around as well.