Before you void your warrenty by unlocking your boot loader. Try using this RUU installer to flash the phone with the stock firmware:
RUU_Kingdom_ICS_35_S_Sprint_WWE_Boost_1.05.653.3_R adio_1.11.00.0418_2_NV_Boost_3.42_0418_PRL61007_re lease_257747_signed.exe
Use the Volume Down + Power button combination to boot into hboot and put it in "Fastboot" mode. This will ensure that the installer EXE will see the phone. (be sure to connect it via USB to the computer and that you have the drivers for this phone installed) Also be sure the phone is completely off before trying the button combination, other wise it may not work.
If something went bad in the data partition or the system partition, then that program will fix it and you will have avoided voiding your warrenty. (since if you tried a custom rom first and later turns out to be a hardware problem, then you'd be SOL when you try to get a warranty replacement)
If the above official RUU flasher doesn't fix your phone, then it's a hardware fault and you'll need to have it sent in for repair or replaced.