My Windows 11 PC constantly behaves as though the middle mouse button is being held down, which makes some games unplayable and makes normal computer use difficult. I've already tried another mouse and keyboard, reinstalled the mouse drivers, restarted the computer, and checked that I don't have any macros configured in my peripheral software. The physical middle button also doesn't seem to respond when I press it. I only have a mouse, keyboard, monitor, and speakers connected, and I'd really like to avoid reinstalling Windows. What else should I check?
2 Answers
Disconnect every USB device except the mouse and keyboard, including controllers, hubs, drawing tablets, and other input devices. A faulty or misbehaving peripheral can generate phantom mouse input. If the issue continues with only the basic devices connected, the next step is to test the behavior in a clean boot or Safe Mode to determine whether background software is involved.
Use an online mouse-and-keyboard input tester to confirm whether Windows is receiving a continuous middle-button signal. If it shows the button as pressed while you aren’t touching it, check for software that remaps inputs, disable peripheral utilities temporarily, and run a full malware scan. Since the scan found no threats and a second mouse behaved the same way, the problem is more likely a background input utility, driver issue, or another device sending the signal than a physically stuck mouse button.
The tester does show the middle button as pressed even when I’m not touching it, but pressing the physical button doesn’t produce a normal response.

I only have the mouse, keyboard, monitor, and speakers connected, and the problem still happens.