The way firepages set things up by default the username and password for the databases you create will be blank. So when you write your connection string you would just have "", "" instead of putting anything in it. Have you changed any settings or configurations since you installed phpdev? Or have you tried connecting with both of those blank?
And when you say it was unavailable did it say something along the lines of that mysql was unavailable? Don't forget to start mysql before you connect to it.
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