How do you know it's slowed down to 40 FPS? I am asking because it's normally just games that have a facility to show frame rates, the only type of applications that I can think of were frame rate is an issue would be media players and games.
In media players, you have to have a steady frame rate to be able to watch stuff so I am guessing it would just be games were you have an issue.
Having said all that, 40 FPS is still well more than you need to give the illusion of movement full motion animation is normally 29 FPS, but obviously none of this helps you out.
CPU intensive tasks
When I get lagginess the first thing I nornmally do is get up task manager (
Ctrl+Shift+Esc), go to the processes tab, and click on CPU, so that the most CPU heavy processes are at the top, that usually give a fair idea of what is hogging resources. Things like your anti virus doing a scan or an update usually impacts quite heavily on system responsiveness, in addition system stuff like windows indexer are notorious hogs.
You mention drivers, I have passed experience of drivers heavily impacting frame rates. My previous graphics card was a Nvidia 260, and I was having terrible trouble with lagginess and extremely slow frame rates, even with the setting down low, just dragging a bar on the side of a window slowed the system down.
It eventually turned out to be a driver issue, but not the graphics driver like you'd thing, it was the audio driver. Windows had just installed the generic MS audio driver, when I eventually installed the proper driver from the manufacturers web site it was like magic, everything was a lot freer and smoother. So maybe make sure all your drivers are up to date.
Another thing maybe to look at if you are getting issue while using applications, like you say with Chrome, is that your cache is set up correctly. Go on-line and check out a how-to on cache set up, the reason why I say this is because you get 'tearing' when moving around applications sound like a disc access thing, maybe windows is trying to load stuff from disc when it should come from cache.
How much memory do you have? If you only have a limited amount of RAM then windows would need to resort to using disc storage when it got low on RAM, paging stuff out to disc is a lot slower than using RAM, and would result in performance issues. If the worst comes to the worst, you could just back all your important stuff and re-install windows, but that's being defeatist.