My air conditioner had ice on the hose outside, the tech said to change the filter, turn the fan off for 3 hours and then turn back on. We did this and now the inside fan does not come on. Now the tech says we need a new motherboard and thermostat?

For one thing, most likely you need to clean the coils and the blower fan if it's very old-over 2 years-and it has not ever been cleaned. A blocked filter will cause it to ice up, too. Until you check the fan motor with a meter you cannot say it is bad; the same for anything else. Until you can put a meter on it you will never know. It doesn't make sense that the fan does not run. Was it running before you turned it off?