I had my fan cleaned recently, but my system still running hard?

My laptop has only recently started working too hard (groaning I call it), and I had my fan cleaned to see if it would help. No such luck. I'm wondering if this is a particular problem with Dell Inspiron 1526 laptops? (On a sidenote, my D drive is very full, so maybe it is causing problems too?) I'm not sure what steps to take next.