Have you logged into the online account (through your browser, not with Outlook) and confirmed that you can send e-mails from there - please do so to make sure the problem isn't with the e-mail provider itself.
If that works out (you can send from the online account), and this just happened and they say your settings are OK, perhaps something happened and a System Restore will set things right. Do you know when this problem began? Try a System Restore to a point in time BEFORE the problem began. Here's the procedure: http://www.vistax64.com/tutorials/76905-system-restore-how.html. Be sure to check the box to show more than 5 days of restore points. If the first attempt fails, then try an earlier point or two. NOTE: You will have to re-install any software and updates you installed between now and the restore point, but you can use Windows Update for the updates. If that doesn't work, then try setting up a new account in Outlook with all the same settings as you think should exist and see if you can login and if this account works properly in terms of sending. If so, it may just be a matter of moving your files to the new account and you'll be back up and running (I'm thinking here the account may have become courrupt for some reason and a new one will resolve that problem). I don't mean a new account with the e-mail provider, just a new account in Outlook with the same settings to see if that works. I hope this helps. If not, post back (with a link to the e-mail provider's web site) and we'll look into other alternatives. Good luck!