iphone wont turn on

My iPhone was glitching and wouldn't load things this morning so I restarted it. When trying to turn it back on, it stays on the black screen with the apple logo. Its been like this for hours. I tried charging it and tried turning it on/off again but nothing will work. I've been clicking the volume buttons and power button to restart it. Occasionally the apple logo disappears, the screen goes black, and then the apple logo comes back and repeats the same process. What should I do to fix it?