HTC One M8 not turning on

I bought a brand new HTC One M8 at the end of December, but it recently stopped working. A notification kept coming up telling me to update my software, so I tried to begin the download but it came up with something like 'You need Internet to perform this update', so I waited for ages and nothing happened. About a day later it finally began he update, but I saw that it was updating just before I got to school so it was about three hours until I looked at it again. When I did though it had come up with a picture of a red triangle with an exclamation mark in the middle on top of a phone. I've tried everything, a soft reset (it just keeps rebooting but never getting the lock screen and then going back to the triangle), a hard reset (which didn't work) and charging it. But nothing I do is working, it's been like this for a few days now and I really need it to work again. It sometimes randomly restarts which is really annoying, but it never does anything else. Does anyone know what to do? I would really appreciate so,e help. Thanks!