How do I use my win 98se cd to reinstall on my dodgy hard disk. I want to reinstall on top to save any data i can. I have a windows back up disc(floppy) I made recently. I am unable to boot up properly as my system has crashed.Therefore it would need to be from dos. I don't know the commands to use..

Put the start-up disk in the floppy drive, then turn on the power. Use the option to start with CD-ROM support. Then you will be at the A:\> prompt. Type "cd E:" without the quotes, this should get you to your cd drive's prompt. (It is usually e since d: is reserved for temporary files. Sometimes it is q, you might have to experiment.) When it says E:\>, type "setup.exe" without the quotes and you should get to Windows setup. Just follow the prompts from there.

you can easily find the drive letter as it mentioned in then bootup. when you get the "A:" prompt see above it, there will be a line mentioning the drive letter of CDrom. some thing like "your cdrom drive is f:"