my i phone wont turn on its shows the apple sign then turns right back off?

i have a 4s and been having so many problems with it... its not under warranty... my wifi grays out its out of the blue said tempature is to hot and now part of my screen has a big yellow spot in top right corner all the way down to about half way but only on right side... then a few mins ago my phone went dead i charged it and now it wont come on all the way... its just showing the apple then cutting right back to black screen over and over... help please??????