It could be it needs to be disabled in your BIOS, but I don't know.
The BIOS is the first place I'd look.
I think most modern computers automatically detect when you put in a new video card and disable the onboard. But there may be some that don't.
Do you think I should disable it from device manager is right above Nvidia... ??
If you can't disable it through the BIOS, then sure, disable it in Device Manager.