We were recently called to look at a wind turbine that was not working properly. The tail was at a right angle to the blades, and it was not making power, since the turbine did not face the wind. The site was great for a turbine, at the top of a hill, with plenty of open area in all directions.
Turned out that the mast was not plumb, and as a result, the weight of the turbine caused the blades to always point down, no matter which way the wind was blowing. We got the site and started pulling on the guy wires, and once the tower was plumb, the tail straightened out, and the turbine started to make power.
It took us a bit, but we got the mast pretty straight, and the cables tightened. All of the cable clamps were loose, probably as a result of constant movement of the tower.
Recommendation: check your cables and clamps every six months!