Hp pavilion p6 desktop won’t start up

[LarsF9]

Suddenly my PC won’t start up any more.

it shows the system start screen with processor, memory, bios version, etc.

it is not possible to enter the bios setup. Nor does it react on window+B. I can press F2 and it says “Diagnose”, but is does not do anything.

what is the next step? How can I check processor, bios, etc??

[TheOldMan]

If it will not respond to the F2 Diagnostics, then it might be more difficult to get an answer.  On an older PC such as that, I like to use a diagnostic disk, if you can get it to boot to that.  You will need a working PC to make the disk.  You can try this link or try a Linux live disk to try to get the PC to boot outside of Windows

http://www.ultimatebootcd.com/

Either will tell you if the hard ware has failed but the Ultimate Boot CD   can tell you more specifically what has failed by running the test routines.

[LarsF9]

It does not boot from CD or USB either.

could it be the processor? Or would that cause an issue during initial startup?

I also tried to flip the RAM modules.

[TheOldMan]

Without beep codes then it could be a power supply.  Look on the back.  Some HP have a green light on the power supply if it is working. 

Troubleshooting an HP Power Supply – Power Supply Indicator Light

Taken from this page  - https://www.pctechbytes.com/hp/troubleshooting-an-hp-power-supply/

Troubleshooting An HP Power Supply

1. Indicator light should be solid and not flashing.
2. If the HP power supply is flashing, disconnect everything inside.  If the LED is still flashing, the power supply is probably bad.
3. If the LED is completely off, then the power supply is probably bad.

[LarsF9]

As described above, the screen shows initial data. I f i remove a Memory bank then I can see it is missing.

also the fans are starting and it seems a check of harddrive is working.

but then it stops...

[TheOldMan]

So we are on the same page, start with tapping the Esc key.  Keep tapping Esc and then press the start button.  Keep tapping until a popup menu shows.  Pick the F2 from that menu.  Does it run  the Diagnostics?