I had the same issue upon initial setup. I'm currently running Windows 10 and no matter what I did, it seemed that Vinylmaster Cut v4 wouldn't detect my SC Cutter via USB. I had the Connection Method set to Direct USB Port and chose Detect countless times in the Settings section below. It wasn't until I switched the Port Type from USB to Direct COM Port that I was able to get it to work. From there, I chose Detect (or Auto Detect), allowed it to run through its tests and the machine finally came to life. It seems counter-intuitive that you would need to choose any option other than USB when using a USB interface, but here we are lol.
Current Setup:
Windows 10
USB
Vinylmaster Cut v4.0
USCutter SC Series