It is easiest to use a boot disk for that Operating System, You will need the proper Windows95/98 boot disk in order to load these operating systems on the computer, also it will reject format because of the incorrect Operating System on the computer.
You have to insert your boot disk in the floppy drive and start the computer.
One time the system has completed booting and an A: prompt appears. You will want to type format C: /s and then press Enter. The purpose of this command is to tell the system to format your "C"partition and when it is finished to copy the system files to the drive. The "/s" switches for "System". You can format a different drive this way by using a different drive letter.