Comment by erdos4d

How is your desktop connected to the switch (ethernet or wifi)? If the computer is wired, maybe you have a virus on it and that is somehow using the wifi to get another IP? I would suggest you backup your user data and wipe/restore the desktop. If it comes back after that, I'd bet someone has cracked your wifi password and is getting in that way, or some other device on the network is the culprit and reinfecting your desktop.