A cooler doesn't do much. My current laptop was working great for over a year before heating issues and all the associated retardness started.
Then from the moment I had it cleaned it worked as smooth as when I bought it, it was awesome.
Just make sure you leave it with someone who knows what they're doing, unless you have easy access to the fan and can clean it directly.
Do NOT try to open it yourself, my laptop went into a coma after I tried to fix it, and gave me a fright.