Speaker setup issue! Help please! :)

My last question (I hope) about my computer setup! I recently reformatted my computer and I cannot get my speakers to work. I for SURE know they work because if I turn them up all the way they make a sound. But I cannot listen to music or anything. I kind of think I need to install something to them. I have Aopen Sound Box 300 speakers and I cannot seem to get them to work. I have no CD for them and I don't have a clue how I can listen to anything at all! I have iTunes open and the songs don't even play. Do I need to install them somehow? Please help this is bothering me so much D:. Thanks!