did you had a GPU of #GreenTeam in it before?
1. uninstall GPU-Driver with DDU in SAFEMODE
3. install either 16.7.3 OR 16.9.2
ps i also have Sapphire Nitro+ RX 480 8G D5 OC and dont have that problem
i also have Sapphire Nitro+ RX 480 8G D5 OC for a couple days , and it shutdown my pc twice allready while playing bf3 , it look like mb or psu goes safe mode and shutdown system , second time my pc didnt turned on before i disconncted power cord for 10 mins . my mb is gygabyte GA-Z77X-UD3H , my psu is Thermaltake Toughpower 650w .
its your PSU -> Thermaltake is shitty - better buy Be Quiet 500W; Cougar 550W; Enermax 500W or Corsair 550W -> these deliver enough power on 12V
but u must be unlucky usually a "shitty" 650W should be enough because the GPU usually only takes 150W while max-load (not furmark)