[HELP] GT-I8552 does not boot after editing build.prop

Hi guys,

HELLLPP!!!

I modified my device's android version in build.prop and also changed its permission to 777. After restarting my phone, it doesn't get past the boot screen. I tried connecting my phone to the PC but it is not recognized. I tried pressing VOL+, HOME, POWER buttons but it still doesn't get me past the boot screen :(

.Any ideas? Thanks in advance.