Live wire touching ground, sends power back through TV cable
I can't answer for Brazil, but in the US, the electrical system is required to be grounded at two places: at the pole transformer and again at the service entrance on each house. Everywhere else, neutral and ground are kept separate.

The cable TV system is also grounded at the service entrance; usually the cable installer simply runs a wire from their "box" (containing lightning arrester, filters, etc.) to either the power meter socket on the outside of the house, or the main breaker panel inside the house.

It sounds like you have a couple of things going on. First, it seems that your electrical system is not grounded at all, so look for the ground stake and check the connections between it and your main breaker panel.

Second, it seems that you have at least one line-to-neutral fault (short circuit) somewhere in your house, either in the wiring or in some appliance. Try to narrow it down by shutting off breakers and/or unplugging appliances in various groups or individually.

Get yourself a decent mains-rated multimeter and check for voltage between neutral and ground at various points; higher voltage will suggest that you are near the fault. Better yet, a clamp-on ammeter will allow you to monitor ground current directly. Worst-case, shut off all of the branch circuit breakers and then turn them on one at a time, looking for problems.