Dell Vostro 5470 problem with GT 740M on Windows 8.1 64-bit

Hi,

I've bought a Vostro 5470 couple days ago.After installing Windows 8.1 64-bit and all drivers listed in 5470 driver's page, everything is working fine except the Nvidia GT 740M. I tried many versions of driver including those from Geforce official site but none of them worked. When I tried to open the Nvidia control panel, it said something like "You are not currently using a display attached to an Nvidia GPU"

Only Intel HD Graphic is currently working now. 

Are there any solutions for this?? Please help. 

Thanks.

Kratu24672