I am on 8.1

I have two machines, both of which have Outlook loaded and both have my email as only email address. The one I normally use has been working ok since I bought it new in the summer, and was working perfectly until yesterday. Today it still recieves email, but any sent messages just sit in the outbox. I have opend and closed everything obvious.

I get no error messages at any point

I have had automated email in the past saying that I have hit my send limit and cannot send any more for an hour (anti spam I guess) but that has always been ok again once the hour is elapsed, and I didnt get the message this time, and the hour is now long past and it still wont send

The other machine is in regular use but has not been used for email since September. It works perfectly, both send and recieve.

I have had a quick look in the settings for both and cant see anything obvious different, but I may be looking in the wrong places. Also they were both working and I havent changed anything on either