Take your phone to the nearest Apple Store or send it to unitedcamera.com both places can fix this issue. The issue is both your carrier and the person who owned it before you. Sorry to disappoint but it's not going to be cheap... :(
Is the disc drive model the same as the old one. You could have installed a non compatible one. It'd be like using Xbox 360 or PS3 controller to play the wii. Also are you sure all the cables are FIRMLY connected?
Based off the picture I found a repair guide you could use if it doesn't work let me know and I will find another. I do not currently have this device, so I can't create one for you. iHome iH8BR Motherboard Replacement