Overview
Is your Raspberry Pi 400 not booting or showing only a rainbow screen? Most Pi 400 boot issues are caused by two common problems: using the wrong HDMI port or a faulty SD card.
This guide will help you diagnose and fix Raspberry Pi 400 boot problems.
Check HDMI connection (most common)
Important: The Raspberry Pi 400 has two HDMI ports, but when using a single display, you MUST use HDMI0 (the port closest to the power connector).
Fix wrong HDMI port issue:
- Locate HDMI0: This is the HDMI port closest to the USB-C power port on the Pi 400
- Disconnect your HDMI cable
- Connect to HDMI0: Plug your HDMI cable into the port nearest the power connector
- Power on: The Pi 400 should now display properly
Rainbow screen symptom:
If you see only a rainbow square or colored screen, your HDMI cable is connected to the wrong port (HDMI1 instead of HDMI0). Simply move the cable to HDMI0.
Note: This issue only affects Raspberry Pi 4 and Pi 400. Older models have only one HDMI port.
Check the SD card
Verify your SD card is properly flashed and working:
- Re-flash the SD card: Write a fresh copy of Raspberry Pi OS using Raspberry Pi Imager
- Use recommended SD card: Class 10 or better, from reliable brands like SanDisk or Samsung
- Try a different SD card: If you have another card, test with it to rule out card failure
See the instructions at: raspberrypi.org/documentation/installation/installing-images
We recommend using the Raspberry Pi Imager software for best results.
Check LED indicators
The Pi 400 LED lights tell you what's happening:
- Power on the Pi 400 with SD card inserted
- Look at the LED indicator (visible through the translucent case)
What the LEDs should show:
- Red LED: Should turn on and stay on solid (power indicator)
- Green LED: Should flash periodically as the Pi reads the SD card
If green LED behavior is abnormal:
- Green never flashes: The Pi cannot read the SD card - card may be corrupted, not properly inserted, or incompatible
- Green flashes rapidly without pausing: SD card read error - reflash the card with fresh OS
- Green stays solid briefly then flashes: Normal boot behavior
If you do not see the green light turn on at all, or if the green light just flashes repeatedly without staying on for more than a second, the SD card is faulty.
Further help
If you've checked the HDMI connection and SD card and your Pi 400 still won't boot:
- Try a different power supply: Use the official Raspberry Pi USB-C power supply (15W/3A recommended for Pi 400)
- Check for firmware updates: Some early Pi 400 units may benefit from a firmware update
- Contact Vilros support: If you purchased from Vilros, call 855-207-9254 or email support@vilros.com with your order number for further troubleshooting