Default [Q] Help with my Samsung Galaxy Mega 6.3

Hey everyone noob here lol. Last night i installed chainfire 3d. After i did that my phone screen went blank. So i restarted it and now all i get is the samsung galaxy mega screen then the part where at&t should show up it just goes blank.Please tell me if their is a way to resolve this i tried restoring factory reset and nothing and i tries keis but my computer won't recognize it. I'm trying to flash it with stock firmware is that the way to go and if so what's the proper way. Thanks alot!