Mum,
Are they emails with pictures attached? Because I suspect Hotmail only accepts upto 2MB of email in your email filing cabinet/inbox at any one time. So if you have previous emails with pictures (or are fairly long emails) still in your inbox that are fairly large, you'll need to delete or move them first. Or if your inbox has quite a few mails in it - it may be blocking delivery as there isn't enough room for more.
Love Sammy xx