Help! I have no water!

Out of four sinks, three toilets, two showers, and one tub, none work properly. One shower barely spits water (have replaced shower head on both showers, with no results ) and the other can't keep consistent water temperature. The shower that doesn't get enough water also has a tub faucet that works fine. One toilet doesn't get any water, and the other two usually work well. (have to replace interior tank parts often) The kitchen sink doesn't work at all, and the fridge can't make ice or supply water through the door, although the clothes and dish washer are fine. Two sinks only get a little stream of hot water..... These problems have been getting worse and they seemed to have started shortly after I had the thermostat on the 80 gallon water heater replaced, which is now corroded. I have hard water, lime is everywhere. Do I need to replace a water filter on the water heater, or is this a huge and costly problem? Also, cleaning the screens on the kitchen sink used to provide temporary water.....
Please help as I am scared of losing the only shower that kind of works...

 

What type of supply pipes do you have? Galvanized?
Public water or private well?
Please describe your water supply system in more detail, and we'll try to help you.
Mike