need some help

[c4m]

Ok so I played 9 holes earlier this week and drove the ball beautifully, hitting 5 of 7 fairways, and even the 2 i missed were right on the edge, and I had good distance probably averaged 260-280.
Then I play a round today and hit 1 decent drive all day, the rest were low flying hooks most of which went less than 200 yards, it was the most frustrating round of golf I've played in my life I was doing the exact same thing with all my irons too, except for pitch shots and chipping.

I've had this problem a couple times before.. most of the time it starts on the back 9 and I figured I was just getting lazy or something. but I have no idea what was happening today, I was making sure my swingpath was inside out, and I could see that I was hitting most of the balls in the middle of the clubface.

Any ideas of what I'm doing? I use a neutral grip, and here are some old videos of my swing: http://www.youtube.com/user/etsubucs.../2/1UoRHRR-Nes
(since i took these I have changed to starting the backswing with my shoulders instead of my wrists)