The skip is possibly your memory buffer being taxed out, if you have huge spikes when you load a track on to B, try eliminating background processes (task manager has a tab you can watch this on, ctrl+alt+del, if your really new). If it is a memory spike and you cant eliminate anything else, time to upgrade the computer.
If all the memory testing goes well and its running, it could be in the sound card directly (dont know how to test for those spikes) but at that point your stuck with an external usb sound card or if you have a tower internal sound card upgrade.
