Sorry to hear that you're having troubles with your new Raspberry Pi 4!
All Raspberry Pi's are tested before they leave the manufacturing factory in Wales, so a faulty Raspberry Pi is quite rare!
Below are the most common reasons for a Raspberry Pi 4 not to work as expected:
- Wrong HDMI port - The Raspberry Pi 4 has two HDMI ports (seen below). The connector on the left marked "HDMI0" is the primary display, so you'll need to ensure this one is always plugged in.
- Operating System - Only the latest operating system release will work on the new Raspberry Pi 4 (at time of writing NOOBS v3.1.1). This will also need to be a fresh install, not used with a previous model of Raspberry Pi. Your options are..
- Power Supply - The new Raspberry Pi 4 needs more juice than previous models - You'll need an official 5.1V 3A power supply (or equivalent).