For the Raspberry Pi 4, note the LED light. The Raspberry Pi 4 LED status indicator will be flashing green regularly when there's SD card activity. Steady red means power is working properly. If the red power LED is blinking, there's an issue with your power supply. Likewise, if the red power LED doesn't turn on at all, it's not connected correctly. If the Pi red power LED is on buy the green LED does not flash, a proper boot code hasn't executed. In this instance, make sure that there's a compatible Pi 4 image on your microSD card, and that the SD card is properly inserted. Then, certain green blinking patterns indicate various issues. A single green LED flash might mean you'll need to use a 4GB card or larger, and use the latest software. Two flashes means the SD card can't be read.