I am using a raspberry pi 4 with librelec flashed on the sd card. When powered on with hdmi connected already to the tv, the rgb screen with all the colours display, but then it goes black and the signal goes off. Even when trying to connect the hdmi after it has completely booted(by watching the ACT led, tried this method cuz read in some posts), the rpi4 is detected by the tv but no signal. ANy help?