1. do your devices need USB 1.0 or 2.0? 1.0 is old standard. 2.0 may not be supported in older PC's.
2. USB provides 5volt to power some devices and that part may have burned out.
3. We assume that USB support is "enabled" in "setup" (enter this at boot).
4. If the device is ok and enabled, W98 automatically detects it and installs drivers (W98 install CD may be needed). If the device has failed, W98 won't detect it.
5. harware detection-install usually doesn't happen under safe mode. You could try safe mode to see if the device is again listed but something in regular boot disables it.
6. an add-in USB port card can be purchased $$, but if some area of the mobo has failed, it may not work. If this new card works and onboard USB still doesn't work, get a USB Powered hub, to save the card. Then you'd know that one of your devices burned out the onboard USB.