Sewing Machine Not Catching Bobbin Thread?

I currently own a vintage Athena 2000 electronic sewing machine. I need help. The issue I have is that whenever the thread on the needle of the machine tries to grab for the bobbin thread every time I give it a full rotation the thread on the needle constantly stops halfway and does not make the full rotation to the bobbin thread. Sometimes it works and other times it does not. I was wondering if anyone can give me an insight into what could be wrong.