Can't see Flash in browser

I created a small Flash file in Flash CS3 and tested it locally in Firefox and
IE. It worked perfectly. I uploaded it to the site using FTP and I can't see
anything in either Firefox or IE7. However, on phoning a friend, they can see
it running perfectly. I am using Vista on a computer which I haven't used
Flash on before so this is the first time it has ever not worked. The puzzling
thing is that it works perfectly in both browsers locally and obviously isn't
an upload problem as it works on other machines, so I can't think what it can
be. Help! (Please)