Hi,
Windows 8.1 is a pain when it comes to USB. Microsoft have further locked down USB drivers for "Security" which means by default it wont allow unsigned drivers. But you can get around it. Google "windows 8.1 unsigned USB drivers" one such guide is here :
http://www.howtogeek.com/167723/how-to- ... d-drivers/The DipCortex USB drivers you need are here :
http://www.soldersplash.co.uk/docs/DipC ... SB-CDC.zipFollow the procedure to boot windows 8 in to a mode to allow the unsigned driver to install then use the supplied drivers.
I've successfully used the DipCortex's with windows 8 following this procedure