Electrical power disappear and comes back later

If lights are lit or if electric power windows are opened or closed. Problem just developed the car starts well without any complications but problem is that if you switch lights on or try open or close electric windows, the electric power system disappear completely as if there is no battery.

Terminals are fine I checked them. Power will come quickly because the car is running but if you sometimes switch off the engine when that behavior surfaces, the power will also disappear for almost an hour or one hour thirty minutes then returns but sometimes if it doesn't come I have to try switch the engine on and by so doing, power will Just resurface from nowhere.

If you take part of the body to the positive pole of the battery nothing will happen as if power disappears and if you take part of the body to the negative pole the electric system shows presence then disappear as you remove the link to the body. Please help.