Cursor changes then system hangs

When I am on the comp. for awhile my cursor will change from an arrow to an hour glass or to a straight line with arrows on each end and even change colors. It is almost impossible to use the mouse at this point then the system slows down and locks up. I had this problem before and ended up reformatting and it has ran fine for about a month until now. I have a DFI k6bv3+/66 MB with a k62 500 processor 96 megs of ram and windows 98.