Around yesterday morning, I lost service on my phone (I have a Galaxy S4 btw, with an old SD card from a previous phone. So the SD Card as of right now, would be about 4 years old.) So basically, I just thought it was normal, because I had a feeling that the bars would be back within minutes. Fast forward 2 hours later. And nothing. That's when I got a little curious and decided to search up what happened, but I got nothing. So I decided to restart my phone, my 4G came back for a couple of seconds but then it went back to nothing all over again. As of right now, my phone is basically useless unless I use my WiFi. My service will come back, but with no bars showing. It's basically just a gray triangle. What do you think is the problem?