Jim Seymour published in his column in PC Magazine (Nov.17,98, US-issue on page 93/94) the very interesting "The Ultimate Win98 Install Tip":
When upgrading Windows95 to Windows98, the Win98 installation procedure swaps out some of the Windows95 drivers in the current configuration with some newer Windows98 drivers ! It is NOT advising the user on this, and (that is the bad part) sometimes the new Win98 drivers does not work properly !
Jim quotes in his article, that in case of problems, going back to the Win95 drivers solved in most cases the problem.
To check, whether you have been the victim of such a driver swap during your upgrade, check the "Version Conflict Manager (VCM)", which you find your Windows98 menu:
Start / Programs / Accessories / SystemTools / System Information:
Microsoft did a good job to hide the VCM, because once you located the
"Microsoft System Information", you continue in the menu:
Tools / Version Conflict Manager:
On my system, I only found an old Mouse-driver
(Windows95 did not know about the IntelliMouse, but Windows98 does and replaces the drivers installed from the IntelliMouse Setup-floppy with its own driver)
If you find here a component, which does NOT anymore work after the upgrading to Windows98, you can try to restore it (as per the procedure displayed by VCM).