Sound issues. I have a new pavilion a 6542p pc. The speakers are altec lansing and its 4 speakers

Question

I have a new pavilion a 6542p pc. The speakers are altec lansing and its 4 speakers connected to a larger box. Is this a subwoofer? There is no speaker on the larger box. I cannot get good sound. I did have pretty good sound from them but the volume seemed lower & lower, I've tried everything and have no sound at all now.
Any suggestions?