Microsoft's Windows 98 : Reinstall Windows with a boot disk and from the hard drive  

What you will require to do this walkthrough is 

1. A Windows 98 CD

2. A Windows 98 Floppy Boot Disk

3. A Computer with CD-ROM access

To start this Windows install. First check that the first boot device in your system BIOS is set to the Floppy Drive.

( To find out how to access the BIOS please refer to your motherboard manual or the manufacturer of your computer. (The system bios can usually be entered on boot, usually by pressing the F1, F2, F8, F10 or DEL key. Make sure you save the settings before exiting))

If you are unsure or don't want to enter the BIOS then just test the computer by putting the CD-ROM and floppy disk in their drives and reboot the computer. 

You will know that your computer will/has booted of CD-ROM when the following screen appears.