This quick tip will explain how to reset the Thunderbolt display, the 27-inch external monitor and Cinema Display successor that Apple has been selling since mid 2011. The need to reset a Thunderbolt Display can stem from a myriad of reasons: the inability to detect an Apple keyboard or other USB peripheral, the need to reset the System Management Controller (SMC), no image showing on the display and so forth.
To reset the Thunderbolt Display is actually quite a simple task that involves just four steps: unplug the Thunderbolt cable from the Mac that you have the display connected to, unplug all devices and peripherals from the USB slots and other ports, unplug the AC power cord and leave the display powered off for 30 seconds.
After you have followed the above instructions, you should have successfully reset your Thunderbolt display. You can then proceed to turn the display back on, after the power cord is plugged back in, and then reconnect the Thunderbolt cable and all USB devices and other peripherals.