Suraj
When the computer tstras up go into the BIOS (Hit either F2, F8, F10, F12 or something else depending on your computer model when it boots up) Then change the boot order to CD first. Put in your operating system disc (assuming Windows) and it will load up before it boots the harddrive. You can then install the OS and it will reformat your hard drive. You may want to also make sure you have your Serial key for Windows.Note: You will lose anything saved on your hard drive.