I'm not sure I undertand the mechanics behind a power attack. Is it as simple as holding the LMB down for a longer period of time? If so, how much longer, if not, what else?
Thanks,
http://www.uesp.net/wiki/Skyrim:Combat
Power attacks deal extra damage. They are performed by holding down, instead of tapping, the attack key. A power attack has a chance of staggering your opponent.
You can perform several kinds power attacks, if you use the http://www.uesp.net/wiki/Skyrim:Controls#Movement to the forward direction while performing a power attack, you will execute a dash strike, useful to close distance quickly. Moving backwards will cause you to step back and then strike, useful for avoiding and countering enemy attacks. Left and right inputs can be used to side-step enemy power attacks, and with the http://www.uesp.net/wiki/Skyrim:Sweep#Sweep perk, a left or right power attack can strike all enemies in a forward arc when using a two-handed weapon.