05 gmc yukon denali xl - Help Power Steering Problem

[yukon_denali_05]

I have a 2005 GMC Yukon Denali XL. I went to a local Firestone and received an oil change and a wheel alignment. The wheel alignment felt really good when i was driving it on my way home. As soon as I get in the drive and position the wheel to the left, i lost power steering. The wheel turns to the right side with no problem, sitting still. I put it in park and i hit the acceleration while attempting to turn to the left and it was turning with some squealing. I just for leaks and checked the power steering fluid level - no leaks found and fluid level is fine. The only other thing that I can think of is that the power steering went bad. But there was no signs of bad power steering that would leave to the eventual thing going bad. Also, given that it turns to the right with no problem and gives a problem when turning to the left, is still a result of a bad power steering??
Could it have something to do with the result of having a wheel alignment performed? Could a bad wheel alignment job cause something like this.

I would appreciate anyone's help with trying to troubleshoot it. Anything else that I should be looking for?

Thanks

 

[newdriver]

check the ps pump shaft, might be broken. check evo sensor, too in the steering shaft.