My menu button and home button stopped working. And my notification bar disappeared. What happened?

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My friends have this group chat, and they were sending so many texts it would slow down my phone. I went to clear the texts, but my phone slowed down so much that I had to restart it. Once I restarted it, my notification bar disappeared, and my home button and menu button stopped working. The wallpaper disappeared, and there is no lock screen. I even tried a factory reset, but that didn't help either. Please tell me how to fix this problem, because I can't do anything now. Only my back button works. My phone is an LG Optimus L90.