Here is more Pi 4 troubleshooting to troubleshoot:
As a first step, are you able to access your Umbrel via SSH?
Steps are here to SSH under How to SSH for reference: Official Umbrel Troubleshooting Guide and FAQ
(Also as a note, monitor and keyboard is not officially supported plugging directly into your Umbrel, please unplug these and power down as they can cause instability and can skip to reflashing)
Umbrel is meant to be plug and play, you can simply install and then access your dashboard at umbrel.local from any browser on your local network
On a computer on the same local network open terminal on Mac or command prompt or powershell on Windows then type:
ssh -t umbrel@umbrel.local
Then if it lets you access it try to reboot with the command:
sudo reboot
If it’s not accessible we’ll need to see if it’s detected on your network at all, you can check your router’s device list or use an app like Angry IP scanner to easily scan your network to see if your node’s IP shows up: https://angryip.org/
Your Umbrel’s IP should display next to the host name umbrel.local and you can see if you can reach Umbrel using the IP in your browser’s address bar instead or by SSHing like this:
ssh umbrel@IPaddress
Check to see if there is a green flashing light on your Pi 4. There must be a green flashing light 
to indicate the MicroSD card is being read, if not we’ll need to reflash umbrelOS on the MicroSD card, and then we can plug it back in and try once more.
Steps to reflash are here for reference under How To Install: Umbrel — The ultimate home server and OS for self-hosting
Reflashing will result in no data loss,
For best practice on reflashing you can follow these steps: