Black screen, now it won't start. Tried unplugging, holding on button for 15 seconds, etc.

[SerafinaFortuna]

I was working  when it suddenly went to black screen. I have tried unplugging, holding the start button for 15 seconds, tapping the start button. The light blinks, but that's it.

[Lil_Boy_Blue]

Hi
First:- Turn off the computer, press and hold the PWR button for 4 seconds.

Then - Leave only keyboard and mouse connected, disconnect all externally connected
devices such as Docking Station, USB storage devices, displays, and printers.
Unplug the AC adapter from the computer.

Next - Press and Hold the Power button for 15 seconds to Hard Reset.
Rinse and Repeat

AND/OR - Power on your PC, press Esc (repeatedly), then F2 at the prompt.
Choose System Tests (Fast Test does a 4 minute hardware check).
AND/OR
HOW DO I USE DIAGNOSTICS?

HP PC Hardware Diagnostics Windows is a Windows-based utility that allows you to run diagnostic tests to determine if the computer hardware is functioning properly. The tool runs within the Windows operating system in order to diagnose hardware failures. HP PC Hardware Diagnostics Windows comes pre-installed on new HP computers, but if not on yours, download here:- http://ftp.hp.com/pub/softpaq/sp93001-93500/sp93457.exe

[SerafinaFortuna]

I unplugged it at the computer back, held the start button for 4 seconds, turned it on, held the start button for 15 seconds, then repeatedly pressed ESC for a full minute. Just black screen.  The power button light blinks 7 times, pause, 7 blinks, etc.

[Lil_Boy_Blue]

Hi

https://support.hp.com/us-en/document/bph07107

Power button LED blinks 7 times with 7 beeps

Motherboard/ Main-Board failure

Contact support for possible Main-Board replacement.

[SerafinaFortuna]

Assuming 7 blinks means it dead. Thank you. 

[Lil_Boy_Blue]

Prego.

Caps/Num lock lights = 7 blinks - Sure Start unable to find valid BIOS Boot Block image.

I cannot tell you to write it off, different BIOS makers have different codes, but it may be BER.

Beyond Economic Repair.

[SerafinaFortuna]

Thank you for your help. 

Do you know... I have an older HP Model 20-b323w with a cracked screen. Slow as molasses in January.

Do you know if the mother board / system board is interchangeable with the HP 24-x026?

[Lil_Boy_Blue]

Hi

Unfortunately I do not.

All I know about All-in-Ones could be typed on the back of a postage stamp.

OLD

https://support.hp.com/us-en/product/hp-pavilion-20-b300-all-in-one-desktop-pc-series/5395624/model/...

NEW

https://support.hp.com/us-en/product/hp-pavilion-24-x000-all-in-one-desktop-pc-series/17200066/model...

[SerafinaFortuna]

You're my hero. 
Thank you. 

[Lil_Boy_Blue]

Prego.