Help with Seriously Slow Computer

Every time I do ANYTHING, you name it: lick a cell in excel, open a new program, close a program, try and access a file, literally ANYTHING, I get a spinning rainbow ball for minutes at a time. My emails load at about a 10-15 minute delay from the server. I am so frustrated, because this wait time is seriously disrupting my work flow. I just missed a conference call because my email invite didn't arrive on time to join the call, even though everyone else received it right when it was sent. I have have plenty of memory on my hard drive (I have 199.03 GB left on a 499.11 GB hard drive - that info took me 60 seconds to access, waiting for the ball). I am operating 10.9.5.

Please HELP!!!