Random Boot Loop - S3

[AC Question]

The other day I was coming home from class and my phone was on my school's WIFI all day and I had no problems, but i always turn off my WIFI access if I'm not using it, and that what I did after i left school. Now you can imagine my surprise when my phone which hadn't been dropped, hadn't been wet and nothing of the sorts in the recent days(I had the screen fixed around late June), randomly starts to restart over and over again when I got home and tried to go on snapchat. After taking the battery out and going to the store to ask a service provider employee about it(to no avail of course) I realized that my phone will only work if I turn the WIFI off. Now how would I go about fixing this? I cannot get a new phone because my one year warranty was over in July and it is now the first of October. I need help.