HP, Dell, etc; design the BIOS so you can not OC the CPU or Ram. There is no way to unlock something that has been removed.
They do this because they want that PC to last for ever and not be damaged by some one who changed values that might cause a problem.
There really is no easy way to do this unless you happen to have another OP/SYS disc or are able to install the OP/SYS only from what HP gave you.
You would need to replace the M/BD and reinstall the OP/SYS only. The HP disc will look for the original M/BD and not seeing it may not install thinking that this is not an HP PC.
In the good ole days you could pull your BIOS chip from your M/BD and have it reflashed or replaced.
Just remember that if you do any of the above you no longer, technically, have an HP computer and if there is a warranty left it will be void.
Good luck to you.