Although you state that your CPU should not be locked,unfortunately this is not always the case and you have just got unlucky with your purchase. I am having an overclocking problem with my i5 2500K I can only just get it to 4GHz and it should go a lot higher, but it won't. These things happen.
A bit of info here: Overclock
The temperature thing 235 degrees, what's that?
You do not give much info on the slowness of your PC, overclocking will not really help if the problems are elsewhere, what do you use your PC for?