I installed Windows 10 and all the driver (BIOS included) from Dell site; luckily my laptop is Windows 10 compatible.
2 processes use a little too CPU, I'm talking about "System" and "Windows desktop manager".
When the laptop is not in use these 2 processes eat 4/5% CPU.
I tried to do a safe boot mode and the situation changes since CPU usage is 0%.
Anyone has the same problem or knows how to solve it?