I want to overclock my HP Pavillion.?

If your multiplier is at max, you're not going to be able to do anything. You wouldn't even be able to tell the difference between 2.4 to 2.6GHz anyway. Something like 2.4 to 3.0GHz, now THAT'S worthwhile. Plus it's a Celeron, those aren't made to be performance chips. That's like saying "I want to install nitrous in my Ford Festiva". Look into some of the over clocking forums out there on the web if you really want to consider this for a future machine. But to be honest, a lot of times it's just best to build a new machine than try to overclock a lower performance one.