I'm guessing that you're using something like Outlook Express. (it helps to know these things!). If so, the 'Send' button should be at the top left, underneath where it says 'File'. If it's not there, try going to View > Toolbars > Standard Buttons, to put it where it should be.
Chris. Thanks for your reply. I do mainly use Outlook Express and understand fully how it works. However, using the method I described above it opens Microsoft Outlook, and there does not appear to be a Send button.