Bridge Port Looping...

Hi,

i have a task,
from the Control center to 5 site, each of the site having 1 fiber and 1 wireless link connected to PowerBOX, then to the PC.
my all site setup is as following.

PowerBox:
Ether1 ==> Connected to PC
Ether3 ==> Connected to Fiber
Ether5 ==> Connected to Wireless link

i add ether1, ether3, ether5 into a bridge port with using loop protection, path cost for ether1 & ether5 is 10, ether3 is 80.
but end result shown be there is looping occur.

if there any method i can do layer 2 load balance ???

diagram.png