HELP !! Keep getting message – The server for account “outlook” returned the error (AUTHENTICATIONFAILED) Invalid username or password

I have microsoft office: mac 2011 (home&business) set up on my iMac.  I originally had my outlook.com email address set up on this and it worked perfectly.  Now for some reason its not working so I deleted the email account and tried to set up again, but I keep receiving this pop up window saying the message above ^^ advising that my username/password or security settings may be incorrect. would i like to try re-entering password. Is there any way of resetting my password ?? I have gone into outlook directly to change it but it doesn't work when try to add it to my outlook on my desktop.  I'm going mad trying to sort this out.  All help greatly appreciated !!!