If I start a battle, and I use an energy attack of any kind, most of the time the game will freeze just before impact, and it will loop the impact sound. This bug does not occur every time I use an energy attack, but it always happens before I have earnt enough points to ascend. I have tried playing it using Software OpenGL and Direct3D. I have a fully patched Half Life. I can't find anything that could be causing it, and no record of anyone else having the same problem.