Dell hardware question

[Estotim]

Hi, i have a problem with Dell latitude D620.
Sometimes in the middle of a work the screen turns off. When some music were playing then it stopped. After that i couldn't change the state of caps lock button. But i was able to turn off the computer when holding the power button on. When the computer shuts down, i try to turn it on again, sometimes it boots to windows and i am able to log-in. But sometimes the computer turns itself of. All the keyboard lights will turn on, power light will turn on, for a moment wifi light turn on, but turns off after that(all this takes less than second) and bluetooth light will light up. The lights stay on for about 4 seconds and then the computer turns off.
Inner fan does not work, but i don't know if this is the problem, as in windows the heat of processors are mostly 30-50 degrees.

I am very grateful if you can help me.
Best regards, Timmo.

 

[Estotim]

I forgot to add that when i try to turn on the computer again and when it turn's itself off after some seconds then the screen doesn't shows nothing. I can't see even dell logo, it's only black.