You need to know the make and model of the PC or the mother board. When you take the Nvidia card out and reboot windows should enable the onboad card, however it might not install the correct drivers so you will have very basic funtionality. At that time you will need to get the correct driver for the onboard video.
Normally its as easy as going to the intel web site and using the automatic update tool. Of course that assumes your mother board or cpu has an intel onboard gpu.