I got a new pc and my monitor only has vga so can i use my old hd2400 to drive the display and my new gtx1070 to game and render?Or do i have to get a adapter?
It doesn't work like that. You can't send the output of the GTX1070 to the other GPU. You have 2 options: get a new monitor (with a displayport input) or get a Displayport or HDMI to VGA adapter. Don't get one of the cheap ones - it won't work. You need an "active" adapter. The active adapter converts the digital video signal coming out of the GTX1070 GPU to an analog vga signal. Here's an example: https://www.newegg.com/Product/Product.aspx?Item=N82E16812119556&cm_re=active_hdmi_to_vga-_-12-119-556-_-Product
Why exactly do you want to do this? I think it would be better to just use your gtx1070 for all your monitors. Also, you may have trouble getting drivers for both cards to work together.
It doesn't work like that. You can't send the output of the GTX1070 to the other GPU. You have 2 options: get a new monitor (with a displayport input) or get a Displayport or HDMI to VGA adapter. Don't get one of the cheap ones - it won't work. You need an "active" adapter. The active adapter converts the digital video signal coming out of the GTX1070 GPU to an analog vga signal. Here's an example: https://www.newegg.com/Product/Product.aspx?Item=N82E16812119556&cm_re=active_hdmi_to_vga-_-12-119-556-_-Product