You probably cannot format the hard drive that contains your Operating System(windows, Linux, Mac OS) from the same drive. Meaning you either are trying to install a new hard drive to get more storage which will not affect your computer's normal operation. Or you are trying to install a new Operating system on your current hard drive which means you will loose all your files if you have only one partition, or just the OS on drive C: if you have more than one partition. Whatever you do try and backup everything on your old drive to a dvd or online storage just in case. If you are not sure what formatting is, you are better off staying away from it as far as you can.