Uh...it's an HP? Don't try and overclock the thing. If you're serious about OC-ing, build your own computer. The problem probably lies in the mobo itself. You would need to get a different one I think
HP along with just about every other name brand pc maker has set their bios' up so that you can not overclock them. This is done to prevent warranty service calls being done, and then finding out that you overclocked and burned up the processor or motherboard, followed by complaints that you voided the warranty by overclocking in the first place.
Overclocking is something that should not be taken lightly. You can do serious damage to your system if things go wrong. My suggestion is to spend the money on the faster processor and better cooling. Your less likely to have problems that way.