Dell Notebook turns shortly after start off (few seconds)

Hello, i own an Dell C640 and have problems. Last night the Notebook turns shuddenly off and as i wanted to strt it again, it only start for a 2-3 seconds. Today i turned it off. The OS boot but after a minute the notebook shuts down again. As i tried to turn it on again, it start again only for 2-3 seconds. I let it for an hour on the table to get cold (it was not realy warm but now its realy cold) and try to turn it on again. I have the same problem. It only start for 2-3 seconds. Sometime some seconds longer, somethimes only for a 1/2 second.

Where could the problem be? I am good in working on notebooks. Is there an other chance then buying a broken c640 notebook and use its mainboard?

 

Are you able to boot up in safe mode? Do you hear any weird noises in the HDD area?

 

There is no safe mode. Its not a software problem. Maybe BIOS, but i dont know. I think you mean safe mode from windows. The notebook shut down after one to 3 seconds. There is no time enough for the bios itself to start.
The problem is always there. Somethimes it boots some seconds longer, sometimes not.
There is not difference between battery mode and AC mode.

 

I have build out dvd-rw drive, wlan, 1 of two ram, hdd....
There is still the same problem

pleease help