Start your computer from a Windows 7 installation disc or USB flash drive.

If you have created Boot-able USB Flush drive go to next paragraph if not 

You can download it using following link:

Download Windows 7 USB/DVD Download Tool 

To start Windows 7 installation disc or USB flash drive
I.Turn on your computer, insert 7 installation disc or USB flash drive Windows, turn off the computer.
II.Restart computer.
III.Press any key when prompted to do so, and then follow the on-screen instructions.
IV. When the page appears Installing Windows, click the Install Now button to start the installation process or click Repair your computer to access the System Recovery Options.
V.Follow instructions.




For more onformation please visit directly Mycrosoft support.

Additional information

What is the difference between BIOS and CMOS?

What are the F1 through F12 key's?  

How to use system recovery options in Windows?

Random black screen while playing games

How to Delete and Clear Recent Items in Windows 7 Jump Lists

How to enter the BIOS or CMOS setup

What is the difference between BIOS and CMOS?

What are the F1 through F12 key's?  

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