Check your steering to see if anything is coming apart to cause a bind, Idler arm bent making contact with the frame, steering stops binding against eachother, any combination of steering link damage or super loose.
also check if one of your CVs is popping out of it's cup, that will cause a problem like you're describing. Check your steering shaft U-joints for play because if they drop out of the yoke half way you can't steer. Lastly check your power steering system, if you're driving with power steering and it suddenly stops pumping it can feel like it locked up just because it drops that load on you.