Help! sudden intense FPS drops on several games

Gateway M-6864FX
Core2Duo T5750 2GHz
4GB RAM
ATI Mobility Radeon HD 2600
Vista Home Premium SP1 x64

I have tried just about everything I could think of to fix my problem, and I am finally out of ideas.

Ever since about a month ago, my laptop (Gateway M-6864FX) has been giving me episodes of random FPS drops in many of my games. These games include Team Fortress 2, Left 4 Dead, Dragonica Online (MMO); it seems to me so far that only games with 3D graphics are affected by these FPS drops. For example, my laptop can normally run Left4Dead at around 30~70 FPS; however, after I spend some time playing the game (usually around 5~10 minutes) I usually encounter the first episode of the intense FPS drop. During this period of FPS drop, the FPS drops down to about 5~20 FPS, and it usually lasts for about 30 seconds~1 minute. One thing I noticed about this FPS drop is that the FPS actually seems to cap around 20, never going above 21 or 22 or so even if I am staring at a wall with nothing going on in game. After around 30 seconds ~ 1 minute, the "FPS limit" suddenly lifts, and the game all of a sudden runs at very high FPS for a few seconds, at around 90~100 FPS. After the few seconds, the game resumes to run at normal FPS, until the FPS drop happens again a few minutes later.

I have first tried reformatting the laptop, but the problem did not go away; I have tried disabling every non-microsoft related services (except steam) and every startup apps (except steam) on msconfig and running the game with no success; I have tried installing the latest graphics driver offered by Gateway (which happened to be a few YEARS old) to no effect, and I also have tried modifying and installing the latest graphics driver for the desktop version of the card from ATI, also with no effect.

I can't think of anything else to do about this problem... perhaps this could be signs of impending GPU failure? it would be greatly appreciated if anybody could offer advice to help me out with this problem. Thanks!

P.S. I forgot to include another bit of info about this problem: during the periods of intense fps drops, nothing is actually spiking; neither CPU or memory usage indicate any kind of spiking.

Thank you for taking your time to respond.

I am using the game's built-in feature; for Left4Dead, I used "net_graph 1" to monitor the FPS.

During the time of low FPS, the game is still technically playable, but the game is simply too choppy and unresponsive to play. (Though now that you've mentioned it, I realize that it is strange that the net_graph would refresh at normal rate while the game is so choppy. Hmm.)

I've updated the directx to the most current version after the reformat, and the graphics driver is up to date.

Download the programs "Fraps" use it to see your fps, then clean your laptop for dust like stated by VampyrByte and I, it is most likely a heat problem. Also download GPUZ(not sure if it supports your card, try it though) , and post the temperature you get.

Haha that's great news, but usually catalyst A.I. helps ..but in your case it's different, also don't force the settings (like AA) in the catalyst program so you can use settings in games instead, maybe that's another thing you did and so the fps with your friend is difference