gdfs is a n independent for each phone in other words like persons name so you cannot change or put other phone gdfs in your phone even though it is k750 phone, if you have meddled gdfs of your phone then you are in soup, XS++ is good, hope you have not backed up your gdfs of your phone, before doing anything we have lots of tutorials in top sony, you need to read tutorials in top sony and then try flashing, now you need service cable to unlock and setool software or you can buy credits to correct the damge. good luck. please read tutorials!