Lenovo T400 / T500 :: Black Screen On T420s And No Boot

I have a T420s that I bought a couple weeks earlier, it's a used one, so there's no warranty with it, I used it several days without any issue, I don't use it very frequently as I use my corporate one most of the time.

Someday when I wanted to turn it on, it stacks on a black screen and it beeps one beep then two other, nothing showing on the screen not even the thinkpad logo at startup, I thought it was a RAM related issue so I put the one from my corporate PC but without any luck, so I wanted to see if its graphic controller issue, I plug the VGA cable on the laptop and my TV and here I can see the thinkpad startup logo but after that I see a message on the screen telling :

"Real Time Clock Error - Check Date and Time settings. Press Esc to continue or F1 to enter setup" and when I press either one nothing happen at all, still stacks there.