Sound on the picade seems to just automatically decrease down to 0 (no sound) after a few seconds

Hi,

I've just finished building my picade a ordered several months back.
There is sound, when i turn up the volumn by pretty the 'volumn increase' button. But after a few seconds, the sound automatically decreases back to 0 (no sound).

I've check the wiring with a multi-meter, to make sure that the 'volumn down' button isnt closed (or being pressed without me knowing) and the volumn down button is open (not being pressed)

Does anyone know what could be the problem? or has anyone experienced the same problem?

THanks