1. your PC might be infected with virus or some software clip which eats up too much of your memory.
2. there are not enough harddrive space. You have too much stuff on your harddrive. When memory is not enough, OS will cut off some harddrive space for temporary memory use. You need to make sure your harddrive is not too full.
3.or your memory is really too small and you are running too many multimedia softwares which usually consume more memory.
