How To Switch From Dedicated to Integrated GPU

[Gway23]

I have an HP6510f

A few months ago my buddy installed a Radeon HD 5770 GPU in my computer for me.
Recently my brother kicked the computer, and chipped piece of the GPU, rendering it useless.

My computer has an integrated graphics card (HD 4200)

I figured going from a dedicated GPU to an integrated GPU would be as simple as taking the dedicated card out.
But apparently it isn't.
When I connect the computer to my monitor now the monitor says NO SIGNAL and the computer remains on.
I've tried using a different monitor, same problem.

I'm pretty sure there isn't any other damage to the computer from my idiot brother.
I just think there's a connection problem somewhere.
I remember when my friend installed the GPU he connected some wires coming out of the Power Supply.
Could've been to the 6 Pin Connection that connected to my HD 5770.

What do I do now to get my computer to use the Integrated Graphics Card?
Do I have to connect the 6 Pin somewhere or unplug it from the power supply? I've searched my motherboard all over couldn't find any connection the 6 pin.

Do I remove the 6 Pin? and if I do this where do I connect the wires coming out of my power supply and hard drive?

I have a really basic knowledge of all this, only recently got into computers, any feedback would be appreciated.

I plan on getting a new GPU soon because the integrated one is garbage, but in the meantime I'd like to be able to use my computer.

 

[Gway23]

did you insert the monitor cable in the default video port of your motherboard?

and you have to just remove the card from the slot.
did your friend set the pci-e card as the default VGA adapter in the BIOS?
if yes, set it to the integrated adapter.

Yes I did insert the VGA into the motherboard's port.
I'm pretty sure he didn't touch BIOS when he installed it.
But even if he did how on earth would I be able to get to it when I can't see anything on my monitor