reset mac usb

This is how to reset SMC on most modern Mac laptops, none of which have a removable battery:

Shutdown your MacBook Air / MacBook Pro
Connect the power adapter to the Mac
On the MacBook / Pro’s keyboard, hold down the Shift+Control+Option keys and the Power button at the same time
Release all keys and the power button at the same time – the little light on the MagSafe adapter may change colors briefly to indicate the SMC has reset
Boot your Mac as usual