Make sure there's only about a 5% fluctuation on your 3.3V, 5V and 12V rails. Again, this should be in the bios, but something like speedfan should be able to report that acurately. If you're seeing changes, especially on your 12V rail, below 11V or above 13V then it could be an issue with your power supply.

Do you have a GPU? I was having hardlocks whenever using graphic intensive programs until I bought a better cooler (Zalman VF700-U). You can't expect a company like HP to care much about their cooling solutions.