when you say you've tried reinstalling win98, I assume that you mean, that yu've done this without reformating the drive. when distater befalls me, and plonging the cd in the drive and runing it doesn't inprove matters then I reformat and start all over again, if noone comes up with a better idea, then prehaps try this! Sadley it means reloading everything, as you be starting from scratch.
as for the boys, I found out from my children it doesn't matter how many times you tell them, I always find that something has been installed, apart from tieing them to a chair at least 50ft away from the computer I really don't know the answer?
I hope that someone might be able to help you more, but at least it put it back to the top, so hopefully someone might give a better answer than mine.
But if I do think of a better answer then I post back