Win98 quits, reboots, incomplete logoff

http://www.beyondlogic.org/interrupts/interupt.htm
http://www.pcguide.com/ref/mbsys/res/irq/index.htm
http://www.pcguide.com/ref/mbsys/res/irq/func.htm
http://www.pcguide.com/ref/mbsys/res/irq/num.htm
http://www.pchell.com/hardware/irqs.shtml

I have the same problem??? We have a about 300 pc's and I only have one that just started doing this? Why? I have removed software that is not the same on all the other ones I have looked all over the system but I can not find any conflicts. Thesystem will rendomley shut down and restart. It will some times go to the screen that says " You can now shut off your pc.". It is atx form factor and is supposed to shut down all the way. It just started a couple of days ago.
PLease help if you can.
Chuck