You can go into your motherboard's bios and force the onboard GPU to be the primary.  By default most motherboards disable the onboard gpu when you install a GPU.

I personally do not hook up any displays to my rigs.  I monitor them through a SSH session using PuTTY.  Also, I'm also mining using simple mining OS, which uses Linux.  It's $2/month per rig but has some really nice overclocking and undervolting features as well as a single web gui to monitor all my rigs.