My phone wont turn on even when it is plugged in.

I went to the skate park on a hot day when i was leaving my friend asked if he could use my phone then he told me it wouldent turn on but i knew it wasn't dead cause the notification light was still blinking, ended up going home and plugged it in and the screen lit up and i could use the phone but for some reason the lock button wasn't working. a few days i ordered a new lock button and installed it fully charged the phone and it still isnt turning on im stumped cause the phone will turn on say its charging and then show a green light and shut back off and i cant turn it on even when its plugged in, Any suggestions? im thinking about just buying another one if its not worth fixing it.