most people turn spanning tree on and leave everything as default. did you?
did you define a root by reducing the priority number (increasing its priority)?
i'm assuming you have a stable tree. in order to unblock equal cost links that you desire to make forwarding, you will have to mess with the port costs.
if you don't understand stp deeply, it will most likely have adverse effects on the stability of your tree and even LAN.
you've been warned. ;)