The fact that it continues to function properly with your MacBook Pro means that the E17 itself is likely OK. By chance do you have another Windows PC that you can try the E17 on? Perhaps a Windows virtual machine (VM) on you MBP (running under VMWare Fusion, Parallels or Virtualbox). If you're able to try the E17 and it works on another Windows PC (as well as your MBP), most guaranteed it's something to do with the USB drivers on your original Windows PC. Alas, troubleshooting USB driver issues can be a real nightmare.
Have you installed any new hardware or software on your Windows PC recently, especially since the problems started? If so, can you try to uninstall the software and/or hardware and see if that resolves the issue? I'd also recommend using a registry cleaner like CCleaner from Piriform. I use CCleaner (Crap Cleaner) frequently on my Windows PCs and it definitely seems to help in keeping the Windows PCs running a lot more smoothly.
If on the other hand, you try the E17 on another Windows PC and it too has the same problems, then there is the possibility that your E17 has developed some unique new failure. The fact that it works on your MBP means it's most likely the E17 is fine. Let us know how you make out after trying the E17 on another Windows PC.
Okay so ive just tested it with my windows 7 that is running on my MBP via bootcamp partition and it works fine, in fact it worked as soon as I plugged it in and it installed the drivers.
I've just run CCleaner and tried the FiiO again, but it still doesnt work..
So I may have a USB driver issue?? I have no idea because it picks up the E17 and installs the drivers perfectly fine, it's just the audio that doesn't want to run through it.. I have disabled the realtek sound card and tried to use the E17 but i still get an error message saying that no audio devices are plugged in and have to enable the sound card again..