How can you restore your computer back to factory settings without using any kid of CD?

Okay, you may or may not be able to do this. Let me give some details.

Many computer manufacturers, rather than including a Windows or restore cd, will instead put a special partition on the hard disk that includes all the data needed to restore the system to factory default settings. This is not always the case, however, and so you may just be screwed.

Consult your manual (if you have one) or the manufacturers website on wether or not your system has a "system restore partition" or somesuch & if so, how to activate it. The system restore process varies from maker to maker (and model to model) so it is impossible for us to know exactly what you can do & how to do it without more info.

If you need more help, i suggest starting a new question along the lines of "How can i restore my [insert make and model of computer] to factory settings, and can this be done without a cd?"