You may have a problem.
Because laptop manufacturers sometimes use custom device IDs for their graphics, the installer that you download from www.nvidia.com
may not recognize your 8400M graphics. I'd normally suggest getting drivers from Dell (support.dell.com), but they only offer XP and 32 bit Vista drivers. No use on X64.
If the latest nVidia drivers (Drivers | GeForce
) won't install, it may be possible to mod (modify) the installer to support your device ID. I have never done it.
You could also try updating the drivers manually (browse the updater to C:\NVIDIA\DisplayDriver\310.90\Win8_WinVista_Win7_64\International\Display.Driver, or whatever you get when you try to install the NVidia drivers). I doubt that it'll work, though.
I expect Dell support to be of no help, as they don't support 7 X64 on the Vostro 1510.