Steering Lock-up

[badwager]

While driving home last week in pouring rain I heard a loud sound kind of like grinding and saw what I was not sure if smoke or steam coming from the sides and back of hood. The noise quit I was able to drive home. The next day the steering was locked but key worked and started the engine after a short burst of the unknown noise again. I could move forward or backward but could not move steering wheel.The pump was full of fluid. I'm trying to determine if steering gear box may be problem.I have noticed sometimes the wheel would be locked at first starting but it could be broken loose and then no other problem. The vehicle is a 1993 Grand Cherokee 4 wheel drive with 6 cylinder engine and 51,000 miles.Thank you for any help