Scroll bar use freezing PC.

Scenerio: Win98 on a Gateway PC. When my client uses her mouse over the scroll bar on the right side (IE 5.0 or any other program) the PC locks up and you have to restart (alt-cntrl-del) It does not happen when she uses the little arrows at the top and bottom of the scroll bar. I also notice that when the pc restarts it does not go through a scandisk as it should if it is not shutdown properly. Any suggestions? Help!!

Thanks!