check to see if you've downloaded any recent updates to either windows or to your graphics driver. i've disabled my automatic windows updates because it occasionally interferes with compatibility of a lot of programs. i've actually had maple not work at all with one patch, and my entire computer lag like a '95 model with another one, though they were re-patched by windows later (rolled back the 2nd issue and never updated again).
disabling auto updates means that you will have to manually check what's "required" to be updated and doing it yourself (through windows update manager).
i'm assuming your computer is a desktop/tower. if it's a laptop, make sure your settings are set to high performance and not battery saver.
finally check/think about any programs you have installed just before the lag started happening, and try uninstalling them.
I dont remember installing or changing anything before the lag happen, it just started the next day for idk what reason. I do the same old stuff everyday. Start comp, get on maple, msn, skype etc, browse stuff ( dont think i click on anything bad) and watch some vid.