It could be the motherboard, but it's unlikely. Windows 98 has a limit, IIRC it's 35Gb ish. I've hit that wall and dual-booted into Win2K, been able to access the rest (without '98 seeing it). Windows NT4 can handle bigger drives BTW, but can't handle a USB Webcam.
If you can find a copy of Partition Magic it'll probably work better than FDisk in reporting what you can/can't do.