[JayCat]

One of the most common causes of lag are TSR's (Terminate & Stay Resident) programs.... These are those little pain-in-the-ass things that install on your computer, and automatically start with Windows, and you can't seem to find any way to turn the damn things off....  Usually, they are a service of some type (Services section of Control Panel)...  Honestly, if u aren't sure what ur doing, find your nearest buddy that resembles a member of 1-800-Geek-Squad, and get him to help clear your laptop of all the useless crap bogging it down....  This is just the most common issue... If this isn't it, I'll give ya some more suggestions....

I agree with this answer. Some of these programs can also use some of your network bandwidth.