Look at the bottom of your tablet, a small cable comes out near the HOME button, make sure it's connected to the orange cable. Then this orange cable's connected to the SD and SIM slot at the left bottom corner.
In turn, this SD and SIM slot are connected to USB charging flex. They're in series.
Your SIM slot is not working, then the problem starts from this connection which makes the HOME button not working either. Make sure your USB flex is fully inserted, otherwise the whole serial connections will not working.
Most inexperienced users tend to disconnect everything unnecessarily. In order to change the battery, only the portion of LCD and USB flex are disconnected from mainboard, then an old and new battery can be taken out and in.
I don't know what you did to make the whole serial connections not working.