all-in-one monitor not working

[smiechowski]

my all in one monitor is not working. I'm getting 3 long beeps 4 short beeps, and a blinking light on the front. no picture. I did get one for a second but its not doing it again. model no. 20-c434

[smiechowski]

When it finally powered up it said unsupported adapter installed. what does that mean?

[Max3Aj]

@smiechowski, Welcome to HP Support Community. 

Thank you for posting your query, I will be glad to help you. 
I understand your HP All-in-One 20-c434 is not displaying anything and is giving 3 long beeps followed by 4 short beeps, along with a blinking light and an error message: “Unsupported adapter installed.” Let's walk through what this means and how to resolve it.

What the Beep Codes Mean

The 3 long beeps and 4 short beeps indicate a graphics-related hardware issue, often pointing to:

• A problem with the integrated graphics controller
• A RAM issue (bad module or slot)
• A power adapter or peripheral that is not supported or malfunctioning

What “Unsupported Adapter Installed” Means

This error typically appears when:

• The power adapter connected is not the original or is underpowered
• A USB device or dongle (like a wireless keyboard/mouse receiver) is causing a conflict
• There’s a hardware fault on the motherboard or graphics subsystem

Recommended Troubleshooting Steps

Power Reset

• Unplug the PC from power.
• Press and hold the power button for 15 seconds.
• Reconnect power and try turning it on.

Disconnect All Peripherals

• Remove all USB devices (keyboard, mouse, printers, etc.).
• Try booting the PC with only the power cable connected.

In some cases, users have resolved this by removing the wireless keyboard/mouse USB dongle and plugging it into a different USB port

Check the Power Adapter

• Ensure you're using the original HP power adapter that came with the PC.
• If using a replacement, verify it matches the required voltage and wattage.

Reseat RAM (if comfortable)

• Power off and unplug the PC.
• Open the back panel and reseat the RAM modules.
• If there are two sticks, try booting with one at a time to isolate a faulty module.

If you're not comfortable opening the unit, it's best to visit an authorized service center, the service team will check and assist you. 
Kindly follow this link to locate the nearest HP service center: HP® Service Center Locator - United States | HP® Support
(Select the country from the dropdown menu and enter the city name or pincode) 

I hope this helps. 

Take care and have a good day. 

Please click “Accepted Solution” if you feel my post solved your issue, it will help others find the solution. Select "Yes" on the bottom left to say “Thanks” for helping! 

Max3Aj

HP Support