Microsoft 98SE freezes

I have 98SE operating system, and lately I have been experiencing freezes. It is not associated with any particular web site but at times it will freeze while at a site. Sometimes it will freeze while nothing is open but the screen saver is on. There is sound on my screen saver and one time the sound was reverbing….like it was frozen at that moment and the pc will not let me Ctrl+Alt+Delete or even shut power off at the tower. The only way to shut down is to unplug!! Does anybody have any suggestions as to what the problem is or could be?