Go to Start/Settings/Control Panel/Display/Appearance, select Icon in the Item window, and make sure 'MS Sans Serif(Western)' appears in the Font box.
If not, then select it, and click OK.
If that font already appears in the Font box, then it is probably corrupted. It can be replaced if you have the Win 98 installation CD.
Go to Start/Run, type msinfo32, click OK/Tools/System File Checker, check 'Extract one file...', type sserife.fon in the box, click Start, type X:\WIN98 in the 'Restore from' box (where X is your CD-ROM drive's letter), type C:\Windows\Fonts in the 'Save file in' box, insert your Windows 98 installation CD, click OK, say Yes if a prompt asks if you want to overwrite the existing file, click OK when it says the file has been successfully extracted, and close the 'Windows 98 CD-ROM' window .