Mail doesn't display emails

When I open Mail in Mavericks, the window comes on displaying everything (including all my subfolders) but no emails

There is nothing in "Mail Activity" the shows its downloading messages

My MBP is making plenty of noise, is this going on in the background? Should I leave it run for awhile?

I tried airmail, but it uses so much CPU and cause my system to run hot and I'd just like to use Apple Mail like I have for over 8 years now