Central heating / air condition stop working

[newDIY]

We have central gas heating and electronic air condition that are controlled by thermostat. Everything stopped working suddenly from last Friday. I switched to either cool or heat and turn on the fun, but none of them works. No flow air is out and no noise.

I changed new battery, no helpful. I thought it may be thermostat is out of order, and then bought a new one and replaced the old one. It still did not work. What should I check and I do at the next step?

Thanks in advance!

[Hube]

I 'll assume you have a forced air gas furnace.
did you check the "breaker" at the main electrical panel? Is there a safety switch for the furnace maybe in the vicinity of the stairway leading to the furnace?.It may be in the OFF position.
If the problem was the furnace's breaker, flip it off and the on again to reset it.
if you have fuses for this furnace check to see if the 'link' is separated, if it is, it's blown, and needs a new one.
Let us know how you make out.
good luck.