How to format my computer?

What is your end goal here?

If you want it 'formatted' get gParted, boot from that, format the partition into the file system you want and done.

A totally blank HD, and how blank is blank? Then what? dban will do it. http://www.dban.org/

Before I waste any of my time, or before others waste their time with further answers (although they can if they want), there is no more advice to give you without more information from you.
 
Try this software for your partitioning needs - Free Partition Software - MiniTool Partition Wizard Home Edition

However if you need Windows install media try this link - Download Official Windows 7 SP1 Integrated ISO
These are NOT illegal – These are just the download links for Windows 7 SP1 ISO which is a retail package that offers a 30-day trial period. You need to activate your Windows afterwards with a genuine license activation key to continue using it. Downloading these files from Digital River is absolutely legal and completely free of charge.
 
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