Back up all the information on the desktop PC to another medium like DVDs or an external hard drive. Once you format the PC, it will be very hard, if not impossible, to recover any data that was on the drive.
Insert the Windows 7 installation disc in the DVD drive of the desktop PC or connect the bootable USB flash drive with the installation files to an open USB port.
Restart your computer and enter the Basic Input/output System. The key for entering the BIOS is displayed on the screen when your computer boots and is often either "F1," "F2," "DEL," "ESC" or "F10." Change the boot options to match that of the Windows installation files. For example, change the primary boot device to that of the DVD drive if you are using a Windows 7 installation disc or to the USB flash drive if using a bootable flash drive. Refer to the motherboard instruction manual or website for instructions on how to do this, as it differs between manufacturers.
Save the changes and then wait for the computer to boot. Press any key on your keyboard when prompted to boot from the primary boot device instead of the computer hard drive.
Select the language, time and currency from the Windows 7 installation menu. Click “Next” and then click “Reinstall Windows 7.”
Read the license agreement and then click the check box next to “I accept the license terms.” Click the “Next” button to continue.
Click the "Custom (advanced)" option from the installation type screen. Click on the hard drive shown on the list and then click “Drive Options.”
Click the “Format” option to format the selected drive. Click “Yes” to perform the format. Repeat the process for other drives connected to the desktop PC.
How to Reformat Laptop/Notebook Step by Step
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