Dennis' computer has a Western Digital Passport external hard drive that mounts, but it can't be read it or ejected. Then it crashes the computer. Leo says that it's a USB device that isn't fully mounting. It's probably an issue with either the USB controller on his computer, or the cable itself. Dennis should try using a different USB cable first. Then he should try plugging it into another USB port and see if he can replicate the issue. The USB driver may also be corrupted.