1st what ur hard disk type their are 3 kezi befit format arigek matak kehone the hard drive type is wouldn't allow u to install new Os so u got two choices 1,losing all the files and format it then recover the files 2,there is some software i forgot the name but u can watch tutorial about it which help u to use ur flash drive as ur permanent drive first and open ur pc then u can change the driver type or backup ur file then format it.