If it is just the hinge that is broken (I'm assuming that's what you mean by 'broken in half'), then you will need to replace the center housing. It's a difficult process for a beginner, and can cause problems with the system if done incorrectly.
A video of the process:
https://www.youtube.com/watch?v=dVn_m_OIHUU
Most steps in the process are here: [guide|25071]
In order to reattach the top screen, remove the shell of the top screen as shown in this guide: [guide|25070]
From there, follow the video I posted before.
Take care to not strip any screws or break any grey flaps connecting ribbon wires to the motherboard. I only say this because those were the two main issues I have had while repairing my system. I haven't been able to resolve the latter, and now my C-Pad is unresponsive, so learn from my mistakes.
If this feels above your current skill level, then I suggest finding an electronics repair center to fix it for you.
Good luck.