What is C and D? Partitions or separate hard drives? If separate HD's, unplug the D drive, change the BIOS to boot from C and reinstall Windows 98..

Either way, if you've set the computer to boot from D, why would it try to boot from C? Instead, you want the C drive to boot first..And when that's done, simply repartition, reformat and reinstall Windows 98 using the instructions in the links below. You'll need a Windows 98 boot floppy with Fdisk and Format tools on it.:

How to Install Windows 98 on a Computer with No Operating System (Q221829)
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q221829

How to Use the Fdisk Tool and the Format Tool to Partition or Repartition a Hard Disk (Q255867)
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q255867

Hope this helps.

Grif