I deactivated the sound notifications then decided to reactivate it, now it will not send or receive emails
Are you getting any errors?
A common cause is the anti-virus application. Disable that and see if there is any difference.
EM Client was in Demonstaration mode …The issue was the eM client ‘free licence’, I did not even know there was such a thing, nothing popped up nor was there any notification or ongoing notification that I needed to get registration … eM client simply stopped working … after trying everything I just happened to click on ‘Menu’ then ‘Help’ then 'about 'option this bought up the licensing issue saying I was in Demonstrations mode, I have now registered … NOTE: you can ONLY use 2 email addresses with this particular free licence.
The evaluation mode lasts for 30 days, and will have all the features of eM Client enabled. After that you need to purchase a Pro License, or if you are using it for personal use only, you can register a Free License. This is clear on the download page.
When the evaluation period approaches the 30 days, you will have gotten a popup notice.
It is easy enough to ignore the popup. 
The Free License is limited to 2 email accounts, as per the popup above and also the terms of use that you accepted when registering.
On registering for either license, you are also provided instructions on how to activate it.