The dial will adjust the top tension. As Kat said, the bottom tension is adjusted on the bobbin case.
Before you tried adjusting the tension, did you check two things?
1. Presser foot down?
2. Did you pull the bobbin thread to the top of the quilt?
Those two are the ones that get me EVERY time! ;) Less common for me to get caught on is that the machine needs to be rethreaded...