Sound problem, anyone know?

i m using my sonicgear speaker (2 speakers and 1 woofer) with asus P5KPL-VM, the problem is I hear sound only from right channel... but it is not speaker problem bcuz i tested with my laptop, all the sound system is all right... but when i connected with my desktop computer i got that problem.please teach me how to solve that. it's really makes me crazy,