Latitude E7440 no post, black screen, no LED keyboard, only power LED light up for few seconds and shutting down again

E7440 can't turn on, black screen, LED keyboard is off, other LEDs are off (WiFi & HDD) when push power button it just light up for a few seconds and turns off again, CPU fan and everything is off.

Methods I tried:

1- I followed all steps in DELL (force ePSA, CMOS battery and etc...) nothing and nothing not worked

2- I replaced RAM and changed with another RAM

3- I removed HDD & RAM, but nothing worked

Last night everything was OK and I was able working but I couldn't turn it on on morning, yesterday its happened and I couldn't turn it on, I tried all steps but after a while I was able turn it on again, I tried rest factory BIOS and everything gone fine, first I thought that is software issue in BIOS, I tried multiple restart and laptop worked, but I can't turn it on again

Please help me

Only power LED is showing and working for a few seconds