If you don't have any luck with Ya_Know's suggestion, could always try reinstalling NIC drivers. Had similar prob when trying to install an old ISA NIC - Win98 only installed bits of Novell stuff, and the rest was apparently part of the NIC drivers. Bizarre.

Other than that, maybe try running Win9x setup program. If you run it over top of existing installation, it will install all original files into correct places. It's easy to do, and sometimes sorts out vxd errors and stuff.

It will NOT adversely affect your system, and only thing it might do (apart from reinstall all files from CD) is tidy your desktop icons...

If you want to give it a go, boot from a Win98 booter, choose "CDROM support". Type "d:" (or whatever) to get to your Win9x CD then type setup. You won't need licence key, and all existing drivers will be untouched. If it is a problem with missing files that are part of the OS, this should resolve it.