There is a known problem with the USB stack on windows. This is a cgminer known issue, which is why we recommend a linux-based mining solution and provide the RPI with every BJ. The best you could do is make some sort of a script that restarts cgminer, or better yet windows itself, after mining stops or even just after 8 hours or so.
Hopefully once we get cgminer and the firnmware stable, we can look at possible windows solutions. Windows in general is not a stable platform, which is why most servers on the internet don't use it.
-Phil
You can reboot it by script every 2h on windows like this with python:
import os, subprocess, time
while True:
print("Starting cgminer...")
p = subprocess.Popen("C:\\Users\\my-pc\\Desktop\\mycgminerfolder\\mine.bat")
time.sleep(7200)
print("Terminating cgminer...")
p.terminate()
time.sleep(5)
where mine.bat is what you use to launch it
I've been having zero stability issues so far, though.