Some Laptops or PCs do not supply the correct amount of power from USB port or use propriety hardware/software drivers for their USB functionality.
#1 - Power KVM via USB (no power adapter)
Sometimes for the initial drivers to load correctly, it works best to have the optional power supply unplugged from the unit, once the drivers are loaded in windows you can plug the power back into the KVM (the KVM gets power from the USB ports when no power supply is connected) but the power adapter is optional unless you are adding external USB devices (Hubs, External Hard Drives, etc) to the switch.
(Best Results: Leave systems on with Windows Desktop loaded)
- Disconnect all of the Cables from the KVM switch (including the power adapter).
- Plug in the 1st machine into port 1 (Video First, then USB)
(DO NOT PLUG IN THE POWER ADAPTER FOR THE KVM)
(At this stage it should start to load the USB KVM Default Drivers instead of the Unknown USB Device Error)
- After the Drivers are done loading for the KVM, Plug in the USB Keyboard/Mouse into the KVM (It should now load the Mouse/Keyboard) - Verify Keyboard and mouse functionality.
- Repeat steps 2+3 for the next computer(s).
#2 - Power Hub
- Try using a powered USB Hub between the KVM and the Computer reporting the problem.