my thunderbold won't wake up from sleep mode

Yesterday morning when I went to sit down at my desk and wake up my computer, my Thunderbolt display didn't wake up. I normally just hit the space bar on the keypad or tap the finger glide mousepad. However when I did that like I normally, nothing happened. I had to unplug the Thunderbolt display from the macbook pro (8 months old macbook) and plug it back in for it to wake up. Now every time I step away from my desk and my computer goes to sleep I have to unplug and replug the Thunderbolt display back in to get it to work. Help!!