exchange account not able to connect to server

My work email has been on all of my devices as an Exchange account. I have had it synced with my Mail program and my Calendar program on an iPhone, iPad, and MacBook Pro. Suddenly, yesterday afternoon, it stopped connecting and I keep getting the message that the account is unable to connect to server. I tried deleting the account from my phone and re-adding it, but that just erased all of the emails from my phone AND all of the calendar entries. AND it still won't connect. Is there anything I can do to make this work again? It is really necessary for my job.

Thanks!