when i turn on my mac, i get this message: USB OVER CURRENT NOTICE A usb device is currently drawing too much power. the hub to which it is attached to will be deactivated. This happened since i had my one to one lesson and brought my imac home and plugged everything into it again. nothing new has been added. i just click on the OK button when i get this message. does it hurt anything? any suggestions what I shld do?