Autocomplete problems aren't common but you may have received some file corruption.
The first thing I would do is a "Scanreg /restore". It should revert the registry back to a time when things worked correctly. When you run the command, you will receive 5 different registry backups to use. Choose the one that worked.:
How to Manually Restore the Windows 98/Me Registry
If that doesn't get it done, then Windows 98 has a small utility called System File Checker which can find and replace "corrupted" files...
Tips & Tricks--Checking your system files for problems
Hope this helps.
The other day I cleared the Auto-complete forms and user names. For some reason the Auto-Complete function does not work anymore, even though it is enabled. It stopped working right after I cleared everything. Im using Win98. Does anyone have any ideas why it is not working?