Bob too many things to list...
can you describe the enviroment your computer is in?
also can you tell us whats in your system? AMD, INTEL..
Last thing you did when you noticed this happening..
Also get your system into safemode.. if everything is running smooth and no hangs then you've narrowed it down to software.
Quote from: Computer Hope
"To get into Windows 98 / ME safe mode as the computer is booting you press and hold your "F8 key" on the top of your keyboard or press and hold the left or right Ctrl key as the computer is booting. If done properly you should get into the "Windows 98 / ME Startup Menu" similar to the below screen example. In this menu choose option 3 by pressing the 3 key and press enter.
Note: With some computers if you press and hold a key as the computer is booting you will get a stuck key message as the computer is booting. If this occurs instead of pressing and holding the "F8 key" tap the "F8 key" continuously until you get the startup menu."
http://www.computerhope.com/issues/chsafe.htm#01