Lag issue/FPS Drops with Windows 8

[Some Nolife]

When I first start AC my fps is around 120-125 and within about 10 seconds it drops suddenly to around 57-60. The multi-player game is choppy for me now as well. I got this new razor abyssus mouse and have it set on 120Hz and 1800 dpi. The mouse makes the game super choppy on 1000Hz (the other setting), so I know it's not that, because I'm ofc using 120Hz. I am just wondering if anyone might know something that could help my FPS.

G-Card: Intel HD Graphics 4400, up to 1884 MB Dynamic Video Memory