Hello, Ewan Gaynor
Welcome to Microsoft Community.
Cause of the problem: The CPU power supply is self-protecting, and most of this problem occurs in the host device. The monitor does not receive the monitor signal from the host at this time. Please observe the fan in the chassis and the power supply is rotating. If this is the case, the cable may be loose or there may be a signal problem on the motherboard. The following steps require you to do it manually
1-Please check the cable connection:
Make sure all cables are securely connected to the monitor and computer. This includes the power cord and any video cables (HDMI, DVI, VGA, or DisplayPort).
If you have another cable available, try using it to troubleshoot the cable fault issue.
2-Unlock the self-locking state of the computer
Some brand machines have electrostatic protection devices that will lock themselves when encountering abnormal conditions. Measures to be taken: Cut off the power, unplug the power plug, and then press and hold the power switch (or press the power switch a few more times). This will also clear the self-locking state of the computer.
3-Clean the dust on the chassis to avoid static electricity
If you use a computer and never clean the dust, dust will clog the ventilation channels, causing the generation of static electricity and causing boot errors. Measures to be taken: Cut off the power supply and clean the electricity.
Finally, I also recommend that you observe the color of the power light. If it does not light up as expected (green light or white light), it means that there is a problem with the power supply and hard disk of the host, causing the power-on self-test to fail, and then it cannot start. If it is this kind of hardware problem, I also recommend contacting offline maintenance. If the host device is also Dell, you can also consider asking Dell’s after-sales support.
Feel free to let me know the status.
Chandy |Microsoft Community Support Specialist