Formatting may be uncalled for. There are plenty of ways to get around Windows not booting. If you give us the information it gives you, then it may be of some help. Things like error messages, or how far the boot process gets will help muchly! Not to mention tell us what Operating System you have etc... Repair options for Windows 98 differ greatly from Windows XP and so on.
In the meantime, get a Windows 98 startup disk and boot into DOS. (If you have Windows 98 or Me). At the command prompt, type:
scanreg /fix
This can fix many boot problems and is worth trying out.