Windows 98 SE shows processor usage 100%

I have two machines running Windows 98 SE, both show processor usage at near 100% when machines are sitting idle. One machine is a P3 550mhz, the other a Athlon 750 mhz. The Athlon machine shows processor usage lower when opening and using applications, but when all programs are closed usage goes back to near 100%. Neither machine used to do this. I have tried various combinations of limiting programs that load on start up. Nothing has resolved my issue, any ideas.