I have an old Windows 98SE system with PentiumIII processor and 128MB RAM.
Some time ago I added a USB2 hub to one of the available PCI ports. Until recently it was working fine.
However, it now seems that any devices I plug into the hub don't seem to be recognised by the system. I know that power is flowing because all devices light up when plugged in. Its just that no info seems to be getting through to the computer about the devices attached.
Any ideas?

Is the card updated to run usb 2.0? That's the only thing I can think of.

You could also try sticking it in a different pci slot.

I am not sure about this... but I don't think Win98 SE comes preloaded with any drivers like Windows xp. Have to installed all the drivers for the stuff that you installed?

Yes to both

Did you check to make sure that the card is still seated properly?

what kind of devices are you trying to plug in? do they work when only one is in at a time?

Have you tried reinstalling the drivers via the Device Manager for the USB PCI card?