The option to activate or deactivate dedicated GPU in BIOS may not be available if your CPU doesn't have any integrated GPU on board my question is what type of CPU are you using are you sure it has integrated GPU cos not all CPU has integrated GPU you have to figure that out first
I do have a gpu on board "hd graphic" and it works when i unplug dedicated gpu but can't make them work together as , my cpu is i7 2600