I recently got also a new PC with Win8.1 and installed the MicroLite after years of flawless connection to a Mac.
It works with the PC but yes, I once experienced the same as you, microlite was not visible in Nuendo. I suspected my very long USB connection, I run 8 meters from the PC to a powered cheap USB hub, which supplies the MicroLite with power. So I disconnected and reconnected the USB cable from the ML and restarted Nuendo, and it was running again. Never had the issue again, but I do not use ML daily, if it comes back I will let you know.