GFX issues with the 8800GT & COD4 (mplayer)

Hi everyone  

I'm desperately seeking solutions to fix my GFX issues i've been having with Call of Duty 4

I'm running an Intel 2.4ghz Quad Core, 2Gb Axe gaming ram with a 8800GT gfx card & i get a terrible frame rate when
playing the game online...the funny thing is it wasn't always like this, my system had happier days running the game
smoothly at decent GFX settings

my game's avg. frame rate used to be at +- 200fps

now it runs between 15 - 35 fps

when i open the game for about the first five to ten minutes it runs fine and hits its maxfps limit (which i hav now set to 125fps) quite consistently, then i get spikes where the frame rate drops into the red...and then ultimately my frame rate does a titanic and sinks down into the red pits of laggyness and unplayability...i would like to remind you all that i have set the GFX on its lowest settings, including texture settings & details on 1024x768 ...and still NO CHANGE!

so i'm stuck here now with a decent PC that is more than qualified to run COD4 like butter but simply won't

...before i submit this to the abundantly intellectual cyber community I'd like to add that yes i've tried everything that can be tried with setting my GFX in game...iv also tried disabling the vertical sync (this once resulted in better fps in CS1.6)

So discuss this amongst yourselves and please help me try reach a solution
end result being me pwning COD4 online with no problems

I eagerly await your responses

many thnx...

theguy_