Problem with central heating - help?

There are a couple of things it may be. But since you say you have no heat I would check this first, you have a circulator pump ( it looks like a electric motor connected to the pipes) and it may not be working what it does is push the hot water through the system,you may have air in the lines some radiators have a bleed screws which you can open to release the excess air which can stop the water flow,you would do this at every location.You most likely need to call a professional to make the repair. Good Luck