HTC One M8 not starting up

[AC Question]

My HTC One M8 will not fully boot up, it makes it to the screen where it states the name of the model but no further. The phone is stock, not modded or rooted. This issue has occurred following a manual restart, after the camera app kept crashing due to some kind of fault with the gallery app. I have tried several hard resets (vol-up + power) but I keep getting the same result. The vol-down + power combination does not appear to do anything at this point. Please help!!