Bios/disable On Board Graphics/enable Nvida?

My computer is not recognizing my Nvida Geforce graphics card. When i try to install Nvida software it stops the installation and says "Software can not find hardware"The tech at Nvida told me to contact the mfgr of my computer to find out how to use the bios to disable on board video and enable Nvida. I've had my computer for six months, nvida was working fine, then i wanted to add another monitor and that's when the problems started. I could use the serial port on the card and was able to hook up my TV to the hdmi and they both worked great but i didn't want that set up permanently. I unplugged the TV and tried to hook up another monitor to the hdmi ( I bought the adapter serial to hdmi) but then neither of them would work. On the back of my tower i don't have a regular serial for monitor i have a hdmi and i am able to use my monitor on that. Now i am not able to use my NVidia, either port! Hmmmmm