Hp 600 g2 long black screen before boot

[MatinDa]

Hi

 I bought a used HP SFF 600 G2 from a website and when i got it, i saw when i press power button, pc starts(fans and all working just fine) but its stages are like this:

1. I press power button

2.pc noises starts but nothing shows up on my screen and this stage takes like 5 to 10 minutes (my keyboard and mouse backlit are on but my screen is no signal)

3. Hp logo comes and pc starts.

Now the issue is that 2nd stage where it shoudlnt take more than 10 seconds.

Now i want to give u these information so u could help me better with my problem:

1. I have tested taking out my CMOS battery and i checked it is charged

2. I checked with single slot ram and i also used a new healthy memory stick and still NO

3. i took out the hdd and used my samsung 250gb new ssd and i clean installed a new windows 10. But still no fix(note that during the installation of windows, the restarts also had the same 5~10 minutes of black screen)

4.i have tried factory settings of bios and also upgrading it. Still not fixed

5.i checked all the physical parts and no issues found

6.ive tried turning off fast boot and no cure

7. My monitor is connected to my sff by VGA cable and its fine

This is driving me mad. Please help

[MatinDa]

Let me point that the debugging speaker is connected and its working im sure

But there is no beep or errors.

My problem is just the black screen before loading windows

Also i dont have infinite black screen. Its always like 5 to 10 minutes and after, it shows

i am using 3 sticks of 8gb 2666 mhz ram(24gb total)

I have tried all of them single and all was the same

And i tested them all using hp memory test and all succeded