Few days ago, my pc started to freeze randomly in games and Alt+Tab/Ctrl+Alt+Tab stuff like that wont work. So i have to hold the power button and restart the pc. That happened to me in about every game of league of legends i play. So i cleaned some of the dusts inside my pc with a vacuum and cleaned the cpu fans with a tooth brush but after i put everything back, i started the pc and the monitor didnt display anything. But all the fans were working, so how can i fix it???