Do what Ako says, also try setting programs as different priorities such as java to real time or high to give to more of the CPU (I tried this, bluescreened soon after because my laptop hates me, shouldn't happen to you though).
Also try disabling some services running in the background, and check for useless software running if you are not using it. If there has been any software/hardware changes investigate them.
When was the last time you did a whole system scan? They take a while but are very benificial.
Any OS updates recently? Windows has a habit of being its annoying self and updating for no reason without your permission, I had one a few days ago so that could slow you down? Doubt it though...
Have you cleaned your startup directory, and only load essential programs at startup?
Also, it may look ugly but turn off Aero if you are on Windows 7, my friend says this helps but personally I dislike this method...
Also, don't kick your computer, things inside might get damaged. And don't swear at it, it might get offended ;P