Why can't I get sound on my iMac. I checked it and it still doesn't work.

try these:

SMC reset      https://support.apple.com/en-us/HT201295

Zap pram   https://support.apple.com/en-us/HT204063

Hazel, what is your configuration? Mac Model and year produced. Any speakers attached to the computer? Can you provide a screen shot of the sound preference pane showing the output tab?

I hope this helps.

Paul