You can't put an intel CPU on an AMD motherboard.
Intel CPU will only work on Intel motherboard and AMD CPU on AMD motherboard.
Here is a list of supported CPU for your motherboard.
http://www.asrock.com/mb/NVIDIA/N68C-S/?cat=CPU
I would recommend getting a used Phenom II X4.
Are you running on integrated graphics currently?
If so then get a new GPU first.
An Nvidia Geforce GT 640 and GTX 750 or AMD Radeon R7 240 and R7 250 does not require a power connector.