Won't turn on even after I charged it for hours

So I've only recently gotten my phone, last Christmas in fact, and already a small crack from the home button; but that's not important. What is important, is that my phone won't turn on even after charging it for hours.

I've tried the thing where you hold to power and home button for up to 30sec but it didn't work and I also tried the hairdryer thing, which didn't work. It had remained the same black screen with that low power symbol for ages. It happened last when when I was playing a game and it was low on battery so I charged it and continued playing.

It them turned off again from low battery so I waited for it to charge again so I could continue playing my game (bad mistake on my part but yeah), it happened for two or three times until it didn't. Meaning that the signature bright screen with the black apple logo didn't appear even after the normal charging time.

I'm super anxious and worried because this is my only phone with many precious memories (not stored in iCloud due to lack of storage space) and I cannot get a new phone if this one breaks. My family is already poor and they I know the threat was only just something to warn me but I don't want to burden them with paying more money for my phone.

Can anyone tell me what I could do in order to open it again or just reinstuct me in the heating trick in detail in case I did it wrong (the other answer wasn't really detailed and vague).