Re: Arduino Leonardo not detected by Windows
Windows shows the device malfunction error when you previously attempted driver installation and it went bad. So, as a safety measure, uninstall the device from Ports
and the unknown device from USB
category. Do not use any USB Hub. Remove all data cards, internet dongles, etc.
Now, connect the USB Cable to your PC and Leonardo. Wait for some time for Windows to show up the Found new hardware
Follow instruction from Step 1 from this post: Installing Arduino Uno R3 Board on Windows 7