Hold down the power button for 2 minutes for a hard reboot. Next, Try holding the power button and the lower volume button at the same time to reboot or reset.

The phone must be clear cached and factory reset. Take all pics and videos off, and remove the SD card too. Then see if their are any UPDATES that may alleviate the storage issue. Then carefully add back most important to least the apps you want to keep. Try to MOVE them to SD card as much as possible. As a last resort take the phone back if the issue persists. There is another work around from the YOUTUBE or internet where you can convert the SD card INTO the Internal Storage, but that is a RISKY one, because you can brick the phone or mess up the SD from being used again by another SD card. VIC~