Q: I am not receiving any emails

I recently upgraded to Yosemite and everything was working just fine for about a week, but now I am not receiving any emails (since yesterday). When I click on Get Mail, sometimes the progress bar shows some number of emails coming in, but then it goes away, and nothing happened. No emails. Sometimes there is no progress bar either, just absolutely nothing.

I have checked my settings and can find nothing wrong, and I have unchecked the boxes that say Automatically detect and maintain account settings, I have closed the Mail program and shut off and restarted the computer, no change.

My computer is a MacBook Pro 15" mid 2012. I use POP for email.