Reinstall its firmware using Phenoix Suite...
or try this method..
First off, you need to Back up your files and Data first. After that, you can now reset and wipe everything in your phone.There`s a 3 way to do that. The first one is the most effective because it will reset everything in your phone and wipe all your data.
1. The three-finger salute is the hard reset. How to do this? This is how: 1) Remove the battery, and then wait for about 20 min or so before putting it back
2) Press and hold these three keys together -Green dial key, Star key[*], Three key [3]
3) switch ON the phone.
4) Do not let go the three keys until you see the WELCOME screen displayed and just let it complete the boot process
2. This is called a “ normal reset” or a “soft reset”. *#7780# is “reset” or "restore factory settings" (same as Menu>Tools>Settings>General>Factory settings). This resets the ini files, refreshing them from ROM, and should leave user data intact.
3. This is called a “deep reset” or a “hard reset”. *#7370# is “format” Once the command takes effect, the phone’s C drive will be formatted: all data on that drive will be erased with clean default files being written.