I'm guessing from this that you've bought a used car.
You'll likely need to replace your battery soon.
Most intermittent power steering malfunctions are down to having a weak battery.
Cars with S/S need a different (and considerably more expensivve) battery; if yours is one of these, do not be tempted to economise and buy a cheaper one, or you'll quickly have problems with your S/S system as well.
As more S/S cars will by now have had their original battery replaced, checking that the correct battery is fitted should be an essential part of a pre-purchase inspection on a used 500.
Your car probably has got it; the easiest way to check is to look at the panel underneath the heater controls, there should be a stop/start disable button there.
There should also be a quick guide for all the controls etc in the wallet with your handbook. Worth a quick peek.
Welcome and hope you're enjoying your new acquisition. Assuming it's a used 500 with a good few miles under its belt, I would recommended replacing the spark plugs with compatible iridium plugs and replacing the shock absorbers with Bilstein B14s. If it's 4 years old or more, look into replacing the timing belt as well. It's a good wee car is the 500.
OK, well no button means you haven't got start/stop then. Is it a 59 plate car by any chance? That would explain why not, may just have been registered in 2010.
As for the stalling, can you describe the problem a bit more? Where does it happen, how often etc? Then someone might be able to advise.