100% sure.  What you've described is a faulty nVidia chip.

The video chip (it's not a separate card) has failed - you will need to replace the system board.

Can you explain me what do you mean? and how do you do it?

Systemboard = motherboard?

If i have to buy a motherboard , i would buy a new laptop instead. But is there any other solution. I mean how are you sure it is that?

Yes, the two are synonymous.  Given the age of the system and the well known unreliability of the nVidia chips, I'd put whatever you might spend on a board replacement toward a newer system.

Thank you ejn63, any1 else that might give me another ideas of what to try? dell agent?

He is right it is an nvidia chip failure.

But then how will the device manager detect it ???

These things will often work for quite a while in Safe Mode or with normal VGA (Low resolution) drivers before the totally fail.

If you've gotten five years' use out of this chip, you've done well.