Do ensure you are backed up as much as possible firstly.
Whilst no expert my laptop HD made some pretty horrid noises and performance deteriorated badly before it finally died.
Otherwise ensure your anti virus definitions are up to date and do a full scan, then defrag, then error check each partition/HD. Others may well have other thoughts I'm sure, but do the basics first eh? :-)
Think about scanning using Ad Aware or similar.
I also have found this site useful for ensuring there are no other possible issues going on. It is safe so let it do as it likes as you go along.