i used to be able to do it, now it wont let me? all i get is silence
i tried changing the signal flow but i dont think it did any thing

I'm not sure if this will work with your set up but I take the audio out (from the computer) and plug it into the input and press the line in button.. Works well for me. I guess you could even go computer audio out ----> mic in.

I have never used the USB cable with my computer.

thats what im doing now but i get lots of static sometimes. i just dont understand why it worked before and now it doesn't

Could be your cable. I have had a couple RCA wires that have shorts in them..

its my laptop battery. when i unplug the charger the static goes away. weird emf interference or something

Double check your system's audio output settings. I work with a mac, and I know I can switch them from the built in audio sound card, to an external one, so if I switch it, I can't hear anything out of my speakers until I change it back.

Haven't used windows in ages, so I don't think I can help much more than that.