Raspberry Pi 3B+ hardware

[Savetheday]

Hi
How do we check a Raspberry Pi hardware if Raspberry Pi works or not? I have a Raspberry Pi 3B+ it won't boot anymore.It was working for a week.Last time as it works I have to remove it from desk to shelf with HDMI USB keyboard mouse and mini USB power cable attached to it and then instantly it has just rebooted.Now it won't boot anymore it stays with the red light on. There is no display screen and no green light.
Thanks.
 

[Chriss]

Do you checked power supply?

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[llkiwi2006]

Check your microSD card connection

[CJay]

Check PSU (as already mentioned) take it back to the bare minimum, just a PSU and the SD card, create a new SD card if you have a spare card, test.

[Savetheday]

I use as a power supply output 10W 5.1V 2.1A.

[Savetheday]

Check your microSD card connection

How could we do that? There is a 1.8 volt.

[llkiwi2006]

Check your microSD card connection

How could we do that? There is a 1.8 volt.

I meant check if the sd card has good contact, but anyway

All your voltage rails seem to be present. IIRC the power led runs off 3.3V. It's probably the sd card at fault, maybe the filesystem is corrupted, or maybe the card is toast. The pi needs firmware files on the sd card to boot, so if it can't read it, it won't display anything or make leds flash. Try reformatting it or try a different card. If you are really unlucky, it could be that the main processor is goneski and there is nothing you can do.

[TopLoser]

Try reading your SD card on a PC. I’ve had 100’s of perfectly good PI’s returned with corrupt or cracked SD cards.

[TiN]

Vcore is 1Vish, there are few other voltages on Pi3 too.
You see four inductors near PMIC chip. Measure them all, should have life in there. Check for any damaged components under the microscope. Sometimes those tiny ceramic capacitors crack, and short to ground.

Anything get hot? One of my old Pi1's died when overloaded I/O pin with 4.5V instead of 3.3V, as result CPU started to cook. 
Other dead Pi1 was result of PSU reversal . Memory chip had the magic smoke escape. 

[bitwelder]

Did you run the checks described in https://elinux.org/R-Pi_Troubleshooting and https://www.raspberrypi.org/forums/viewtopic.php?p=437084#p437084 ?

[SiliconWizard]

AS others have said: check your SD card first. Try another one. Unfortunately, data corruption can happen pretty easily on SD cards with an  RPI, for instance if it loses power before the OS has completed its shutdown AND the SD card has completed all residual writes. Not all SD cards will work fine on an RPI either - I had frequent data corruption with Samsung Pro microSD cards, but the Evo line was fine.

You can also check your power supply. The RPI3 is a bit power hungry and a weak power supply will make it fail in various ways - RPIs are not very forgiving and may fail with a LOT of off-the-shelf 5V/2A adapters.