Vostro 3405 - Laptop Freeze and then Graphics Driver won't work

The Laptop freezes, without any reason (no programs running). And the mouse and keyboard won't respond. I shut down, holding dow the start button, when I restart (pressing again that button). The graphics drivers won't work (HDMI output, etc). I need to reinstall them and the problem will be solve.

But, why it will freeze and then don't recongnizes the graphic drivers?

PS: Dell Chat Support said that the problem, according to the diagnostics is software related, and won't solve it because of my warranty apparently only cover hardware. But if the problem is software, it's completly their responsability, I mean I download all the drivers from the Dell website.