Upgrading old hp p6000, need help

[DominusOfAll]

So I've had this hp for a few months (was given to me from a friend), and I've upgraded its gpu but the cpu bottlenecks so badly that I can only run gpu bound games and still get frame drops. I'm looking to upgrade from the horrid am3 socket to a lga 1150, but I have no idea what mobo would fit in this case, and I'm wondering if I should just buy a new case/mobo combo. Also the specs are: gtx 960 4gb, 6gb of ram, amd athlon II x4 640, 600w psu. Thank you in advance

 

[BadAsAl]

Find your model at this link: http://support.hp.com/us-en/product/hp-pavilion-p6000-desktop-pc-series/3884665/product-info
Click on the model to go to the specs page. It will tell you the motherboard. Look that up and it will give you the form factor that you need (ATX, microATX, etc.). Then you can shop for that form factor and it should work in that case.