No USB connected, receiving error message "USB devices disabled: Unplug the device using too much power" Recently I have been getting the error message "USB devices disabled: Unplug the device using too much power almost constantly. There has been nothing plugged in for some time, and if something is using too much power, I'm not sure what it might be.

Different problems that have suddenly appeared, but may be related - occasionally won't charge with the MagLite charger; occasionally runs slowly; audio stopped working just today - the little speaker symbol up top is greyed out and it won't recognize headphones or the laptop's own speaker.

It's a 2014 MacBook Air running El Capitan - I recently updated from Yosemite, which did not solve any of the issues but also didn't make new ones appear. I have also tried restarting the computer, resetting the SMC, and scanning for any viruses using Avast Security, which found no issues. Nothing has helped.

Anybody else having similar issues? Thank you for any help you can provide!
This could be a hardware problem.

You have more things connected to USB than you are aware of.  Looking at the "System Profiler" under the "USB" section, we see a number of things:


FaceTime Camera
Bluetooth
Trackpad*
Keyboard*


* Not shown because I am on an iMac



There could be an issue with any/all of these devices or there may be an issue with one of the power rails (the circuit that delivers power to these devices).

First thing to do is run Apple Hardware Test (AHT).  Hold the D key while booting from a powered off state with the AC adapter connected.  Next, try running things in Safe Mode (hold Shift while booting).  If the problem persists, the issue is definitely hardware.