Try pressing Buttons #1 and #6 together, sometimes #2 and #6 works instead. If not, try #2 and #5.

Failing that, get yourself a set of radio removal tools and use them to pull the radio out from the dashboard a couple of inches. No need to disconnect anything.

It will then be possible to read the serial number from the white label on the radio casing.

If you manage to get the serial number and it begins with an "M" then you can use the following link to work out your keycode:

www.pumapeople.com/decode.php

However, if it begins with a "V" then it's a Ford main dealer or someone on Ebay, I'm afraid.