Assassin's Creed 3 sudden slow down

[Micael Ezio]

I'm sorry to bother but I have searching on other forums and still can't solve it. So this is my problem, Im playing Assassin's Creed 3on Windows 7, it ran normal for few months, but recently when I played it, it ran normal at the beginning, but after 30-40 minutes suddenly it slows down, fps just suddenly drop like 10-15 fps after few minutes just for about 3-4 seconds then returns normal. like just there is any other programs running in background, when I posted on forums before, it suggested the audiodg.exe is running, "try to turn off the effects", and Ive done that, problems gone for a moment but after hours it appears again, and now its not audiodg.exe, I checked on task manager and nothing is strange. Until now it still bothers me, Ive updated the graphics and audio drivers, Ive checked the viruses with updated MSE. Iva also have settings set to low I really appreciate any help, thanks before

this is my systems:

Dual OS XP+Windows 7
Nvidia GeForce 9400 GT
4 GB memory ram (2x2gb)

 

[HEXiT]

likely cause is poor temps cause by aging hardware. your lucky to get it to run on such a lowley card as it was very poor for gaming at launch never mind today.
get gpu-z, hw monitor, real temp and speed fan run at least gpu-z and hw monitor while your gaming if your gfx is getting close or over 80'c then you need to turn the fan speed up and more importantly clean off any dust. if your cpu is close to 60 and its a dual core then clean off the cooler and fan. turn up your case fans if you can or add better ventilation to the case. (this doesnt mean take off the side panel as this will destry your air flow)

so yeah check your temps.