|Unless you run DOS programs, such as DOS games, you don't need config.sys to run W98.|
In which case, shut down and restart in MS-DOS, then at the C prompt type:
ren c:\config.sys config.old
Hit Return key after above command.
This will disable config.sys and the system should boot up fine. If you ever want to run programs in pure DOS, rename it back again then fix the problem with the config.sys file.
If you can't get to DOS the way I suggested, then tap F8 key during bootup and choose one of the command prompt options. Another way is to use a boot floppy then switch to the C drive by typing c: (then hit Return).
some other bloke...