If you're seeing a rainbow screen when powering up your Raspberry Pi, please try the troubleshooting steps below:
- HDMI port - If you're using a Raspberry Pi 4 with 1 screen, make sure it's plugged into the left port (labelled HDMI0). Only use the second port when using 2 screens.
- SD Card - Are you using a Sandisk or Panasonic card - we only recommend these brands, cheap no-name cards can cause endless issues
- Raspbian - Are you using a freshly downloaded copy of Raspbian? The Pi4 in particular doesn't work well with older versions of Raspbian.
- Power - Are you using an official Raspberry Pi USB-C power supply with your Raspberry Pi 4? We only recommend this power supply as it has been rigorously tested for use with the Pi 4. Cheap power supplies are a common cause of issues.
- Bootloader - Is your bootloader working? Take your SD card out of the Raspberry Pi and power the Pi back on again - if you see the green LED flashing (usually a pattern of 4 flashes) - the bootloader is fine. If not, see the link below.
- Check the boot problems thread - there is a very helpful and detailed thread on the official Raspberry Pi forum for boot issues including the rainbow screen: https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=58151