Emails not sending – within past day or two

Help! I received emails for new orders, etc 2 days ago…but not emails are NOT being sent. Everything has worked fine before. But now NO EMAILS are being sent!! Here’s the error message I get when I tried to use the “forgot password” — The e-mail could not be sent. Possible reason: your host may have disabled the mail() function. But, order emails are not being sent to me or customers, neither emails for the “contact me”. HELP!