Windows 8 on mac wont start

Hi all i recently installed windows 8 a couple days agoon my 2012 13" macbook pro model and i got no problems with it. I'm able to play some pc games on it with friends. Then for the past 2 days whenever i boot my mac and select it to start as windows, i get the windows logo on the screen and the circle thing spinning then the next thing it completyl dims to total blackness to point where i could only hear the machine parts of the computer running. i dont know what happen. ive tried it twice and the same thing keeps happening. In order for me to get back to mac osx i have to press and hold down the power button until its completyl off then boot it up once more. Can you guys please explain whats happening with it and how could i fix it???