Alot of Phone Issues

My phone is only 4 years old and its having alot of issues,currently it keeps flashing the apple logo and turning off. I saw other articles and it told me to plug it into my computer and let iTunes resolve the problem.But it seems that my computer isn't recognising my phone and I'm pretty sure it isnt the charger due to it working on other devices. How do you guys think I could fix this?

(Another thing that I want to add is that before this happened my phone was already acting strange,it kept turning blue,flashing or turning dark around the edges and then it turned off but it normally came back on)