Overheating and also my steering wheel all of a sudden cannot turn.

did you look to see if belt attached or pump failed

A broken serpentine belt leads to a sudden loss of power assist for the steering system, where the steering wheel all-of-a-sudden becomes very hard to turn. ... A broken serpentine belt stops the water pump from circulating coolant (antifreeze) through the cooling system, and the engine can overheat - anywhere!

have a wheel alignmennt
indicates excessive caster measurement

I have a 2009 subaru legacy. I was driving today and suddenly the steering wheel felt extremely easy to turn to the point where I can turn it almost 360 degrees. Please help! What can I do?

replace the power steering pump.

Ok those problems do not seem inter-related. Seems like you first have a problem with your power steering pressure switch which is connected with your idle air control valve. If your idle air control valve doesnt put more air in the engine when you're turning your steering wheel it can cause your engine to cut off because it is not receiving a signal from the power steering switch. As far as your car overheating, check your coolant reservoir, leaking radiator or broken thermostat.

Try turning the steering wheel (hard) right and left while turning the key. Steering lock , and ignition lock work in conjunction with each other.

Broken drive belt or the reservoir for the power steering is out of fluid !

I doubt it's your 4x4. Most transfer case will start turning the front driveshaft, meaning that BOTH front wheels would try to turn.

Could be a brake pad/caliper locking up on your left wheel. That'll make that wheel turn slower resulting in the veering left.

Could also be a wheel bearing. However usually you'll hear a grinding noise to go along with that. And it'll pull rather consistently in that direction rather than suddenly.

Or, what first comes to mind is that your steering box is loose, or the gear inside the steering box is stripped in one spot. Or your front tie rods could be shifting or possibly ball joints. These would cause a sudden shifting/veering.

All of these things are front end related. And also very dangerous. Take it down to any alignment shop, have them put it on a lift, and diagnose immediately.

Worse case scenerio is that a front end part breaks and sends you out of control and into someone else. Please get it checked. A diesel Suburban could do a lot of damage.

The steering lock consists of a hardened pin and it may not be releasing any more although it shouldn't interfere with the turning of your key, just your steering unless the Geo is done differently.
If it was mine, I would get a little rough with it and turn the steering wheel hard from left to right while trying to turn the ignition key. 
Even disassembly is not easy since the lock area is supposed to be secure so it cannot be easily defeated.