Asus Laptop k52jt and dell u2415

Hi to all,

this is my first post on this forum!

I' ve purachased today a new flammant dell u2415. I love the design and the potential of this monitor!
Actually i haven't a desktop pc but only a laptop auss k52jt with vga and hdmi port.

Today i install the driver of the monitor on my laptop, then i connected the laptop (graphi card -  ati HD6370 M ) to the monitor... but notinhs happens...only the message "no dp cable". 

I thinked :"Why the monitor ask me display port cable if i connected hdmi?"

On graphic card properties the dell appears like the 2 monitor. Iextend the desktop to the monitors (my laptop and dell) but nothing happens...

I've updated the drivers from amd-ti site. I installed the latest catalyst and ... my laptop monitor loose all the brightness! I can view the video only with a torch!

Then i was be able to restore the precedent windows without these drivers.
Then i install the latest driers 8.8.84 of my graphic card from asus site... it was ok!

But nothing changed.
Also with catalyst i can see the dell monitor via hdmi but video don't show up.

I dont' know what i do. Have suggestions?

Do I have to but dp to hdmi adapter? But why hdmi direct cable configuration is wrong?

Thanks

Gabriele