|"when i want to overclock what can limit the process of over clocking?|
You mean other than lack of overclocking knowledge and/or experience?
Generally speaking, overclocking should be done manaully in the BIOS, not thru software, not thru some "single click" BIOS setting. You need to address every setting individually, so obviously you need to know what you're doing & how everything interacts with each other. No 2 CPUs overclock the same, no 2 boards overclock the same. And you need to understand that increasing one setting usually affects several others. For example, when you increase the CPU frequency, the RAM/PCI/AGP/PCIe frequencies will all increase along with it. If you don't take steps to prevent that from happening, they will limit the overall overclock or cause system instability.
If you have questions about overclocking a specific setup, list the system specs.