If your timer is "working" (meaning you can trace it and see that it's printing values out to the log as expected) then it's most likely a problem with the way you've set the font in the text field.
If you're sure the text field's instance name is being invoked correctly (trace out the object to be sure Flash is aware of it, as in... trace( myTextField);// (this should not be null, or undefined, provided you've set the instance name of your text field to 'myTextField'.
If thisis all correct, then it's almost certainly font embedding issues. This is where CS4> have really screwed the pooch. Click on the text field and select a font and then click embed fonts. After you've embeded the font and given it some name of your own ("myArialBold") you'll THEN need to find *myArialBold in the list of available fonts (in the properties pane, not in the fonts dialogue) and select your embedded font.
It doesn't make any rational sense, since you *feel like you've selected the font when you were in the embed dialog, but in fact, that's just where you embed the font into the environment, it doesn't actually take effect on this particular text field till you've selected it from the drop down of all your fonts (where it will now also be, towards the top, above a line where all your own custom embedded fonts dwell).
The upside is that it will now be there for the duration of this project and you can just select it for any text field (and not need to embed it again).
the down side is that if you ever delete the embed but forget to change the association on ANY text field, Flash will complain every time you open this project that a font that's being sought is missing and you will rip out every last hair on your head looking for where this text field is. In a large project, I've seen this lead to people killing themselves. Very sad.
If that doesn't work, we'll need to see more of your code :)