SOS my computer turns off after 2 seconds !! Troubleshooting

Please, I have a little problem with my desktop computer, when I press the start button it turns on (I hear the fan running / no beep) then the computer turns off before the bios starts,

I made the method of elimination always the same issue but when I remove the power connector 4 pins (2 yellow + 2 black) (look at the picture) in this case the pc remains lit but no bios appears
I have a doubt that it is thermal paw but I'm not sure help me please!