I had this problem recently aswell, tried everything I could think of, what I finally ended up doing is copying all the esential files onto another computer over the network and formated and reinstalled windows 🙁 sorry I can't be much more of a help but the computer runs perfect now 🙂.
It could possibly be a registery problem, however I dought it, but AFTER you back up your data try booting to dos and running scanreg and restore the registery to an older version, from a date you remember it working.
That may fix it but Im not sure, hell if it doesn't it will most likely fry win98 anyway and you would be forced to reinstall :Q. good luck.