Building pc for first time and have now confused myself with the form factors

[Surge92]

Im building a pc at the moment and to save money im transplanting parts from my brother's computer he built a while back. I'm using the case and the fans, however despite being able to support an atx motherboard it cannot support the atx gpu(http://www.gigabyte.co.nz/products/product-page.aspx?pid=4890&kw=GV-N78TGHZ-3GD#sp) i would like to use purely because the back panel isn't wide enough it measures roughly(it is very difficult to get a ruler in there) 115mm, the gpu is 132mm so it clearly wont fit through the back panel.

Could someone please explain to me why this is and give me an explanation of the tower(full, mid etc) system for cases.

Thanks

 

[TofuLion]

what case?

 

[Neog2]

Thats a double slot card. I find it very hard to believe you have a case that supports an atx motherboard but doesnt have a second slot next to the PCI-Express cutout on the back panel. That card is made to fit in two panels not one panel on the cutout in the back.

Here is a picture of a dual slot gpu card like the one you listed inside of a mATX case. A smaller form factor.
http://realhardwarereviews.com/rhr_storage/images/Case/Phenom/gpu_inst.jpg See how it fits into two slots.

But there are some goofy cases out there so like the guy above me asked what Case. Brand/Model

 

[Surge92]

Sorry I don't actually know the model number of the case but it was manufactured by Raidmax( the manual has no form of model number written in it or anything to identify the case other than the manufacturer which is rather silly)
but i did take some photos of it.

http://

just to make it fit the two panel gpu i was going to remove one of the plates in between tthe slots.

 

[TofuLion]

depends on how determined you are to save the $60. i, personally, would rather just pay for a new case, but nothing wrong with cobbing it together if it works.