Crackling sound with video on vista

I had moved my pc to another place in my home and when I hooked everything back up now when I watch a video it crackles and gets worst when I put it in full screen. I have a presonus box that my hubby uses to record his music and it is set at default for sound but before I moved the PC the speakers where set at default. I can't get my speakers to play at all unless its under presonus. This is so annoying cause now I can't watch anything because the sound crackling. Could it be the Presonus box? I already changed the RCA cables that go to the box to my stereo for surround sound. I am dumbfounded when it comes to all this technical stuff. I have the Presonus hooked into the PC through the 1394 cable and a RCA cable coming from my Presonus box labeled speaker out and going into the Stereo. When I moved the PC I had a RCA cable with a headphone plug on the other end. The RCA cable was plugged into the Presonus labeled input 3-4 and ran to my pc but can't remember which hole the plug went into and tried sound test and nothing. The way I have it set up now is the only way I could get it to work. But still have crackling when view a video in small or full screen. Can anyone help me?