apple

it has intel on board graphics & amd discrete graphics i believe. how might i go about disabling one or the other - i looked in the bios but can find nothing to change. any one have any thoughts?

I have an i7 E6440. My problem is that I can't get any VGA output. The monitor amber standby light goes green so I presume something is happening but the display stays black. I tried the options I get by pressing the fn & F8 keys as well as the options in the screen resolution menu. Tried other monitors too with no luck. The monitor worked fine on my old Dell M1330 - just plugged it in & it worked on that one right away. HDMI output works fine. Is it necessary to switch from HDMI somehow? I updated intel & AMD video drivers & the BIOS. I checked the manual - no info there. I looked in the BIOS settings & nothing obvious stood out. Any ideas? I guess other Dells will be similar so even ideas from other laptop owners would be appreciated too. Thanks for any replies.