"Cannot connect to server, it may not exist or it is unavailable at this time"????

I Have a 13" MacBook Pro w/retina (early 2015) and earlier I was able to connect to my workplaces server to access the public files within. Now, it keeps going out and giving me that stupid error message whenever I try to connect to the server. All of the windows machines are working perfectly fine on the server. Does anyone know why it's saying that or what I can do to get back connected? I checked my firewall settings and connections are allowed through to my computer...tried almost everything...thanks...