If a computer cannot boot from a USB device but can access its files in Windows, what is the likely issue?

The correct response focuses on the boot order in the system's BIOS or UEFI settings. When a computer starts up, it follows a designated boot order to determine which device to use for loading the operating system. If the USB device is not prioritized at the top of this boot sequence, the computer will not attempt to boot from it, even though it can access the files on that device once the operating system is running.

This situation can occur when the USB device is connected, but the computer is set to boot from the internal hard drive or another device first. Ensuring the USB device is positioned correctly in the boot order can resolve the issue, allowing the system to recognize the USB as the primary bootable source.

The other options, while plausible in certain scenarios, do not align as closely with the symptoms described in the question. A malfunctioning device can prevent access altogether, an incorrect file system might lead to the system not recognizing the device at all in some cases, and a defective USB port would likely prevent communication between the computer and the device entirely.