Why wont my phone turn on?

So yesterday at around 11am, my phone turned off suddenly. I thought that it must’ve run out of battery so I plugged it in to charge but after around 24 hours it still had not turned on. Even when you hold the power on/off button, the battery symbol does not appear. The screen is completely black. I’ve tried countless things such as heating up the back with a hairdryer (this may sound quite stupid but many people said this worked). I’ve also tried to connect it to iTunes to reset it but I need a code sent to my (broken) phone to sign in. I’ve tried but failed to put it into recovery and dfu mode as well. I’m stumped on what to do next so if anybody could help me I’d really appreciate it :)