monitor flashing colors

Hello, I have installed a new motherboard and reinstalled windows, but now my screen keeps flashing in different colors. It only works properly when i connect another screen, but as soon as i disconnect that screen, my main screen starts flashing again. In the past i had the same problem but i...

Apologies for not knowing, but I wanted to know if it was possible to play steam games off a external drive? I heard that it would need to be at least 7200 rpm and usb 3.0. Is it okay? and regardless whether or not it does, can anyone recommended one?