I essentially have this exact same problem. Plug in Helix to PC. Recognize... PC audio starts playing through helix... open HX Edit and it recognizes the Helix. 15 seconds later, lose connection, audio goes back to computer speakers, then at some point audio might go back to the helix, but HX Edit won't recognize it.... and then, after 10-15 minutes of leaving it plugged in (with it going in and out), I get the same message TurbineTester got about "The last USB device you connected to this computer has malfunctioned....blahblahblah"
I'm getting really frustrated with this because I don't understand it. I've worked with computers most of my life, but I can't, for the life of me, figure out why this won't work. I'm dying to know how the USB cable works for you.