Bearing seized on the pump.
It could be from worn bearings on the shaft that the pulley turns.
I would be more apt to believe that the power steering pump failing would have caused the belt to jump off and become lodged between the pulley and the motor than the other way around.
the pulley has to be pressed on and off. so, i would say no.
the pulley is bad when it stops moving
If power steering was an option for that car and it has the same motor you could change it, but it would be expensive. Assuming it is front wheel drive, you would need to change the steering rack, possibly the wheel assemblies, install a pump and change the crankshaft pulley and serpentine belt.
just wear and tear over time will cause the belt to break.but if this is a recurring problem,one of the belt pulley wheels may be out of alignment or bet,you may also be over tightening the belt which will put xcessive strain on power steering pump and cause runout to wear belt more quickly
I, personally, would recommend having this performed by an expert. If you must do it yourself, first you need to clean the area and remove the power steering fluid from the reservoir and the line. Unplug the pressure-switch connector and remove the pulley and install it into the new pump. Rotate the belt and slide it towards the pump pulley.
most likely they were not properly tightened at some point
If an idler pulley is broken, I would advise not to drive it anywhere. It would effect the power steering, water pump, alternator and coolant fan causing you to get stuck on the road and possibly cost many more $$ in damage.
If it was ordered with power steering it would have it.
Most often that's caused by one or more of the pulley's being misaligned. Check the alternator, power steering pump and any other pulley that may be out of alignment. If anyone has recently worked on the alternator, power steering or whatever, make sure all of the braces were put back in place. That's probably the most common reason for allowing a pulley to bend out of alignment.
You didn't mention what vehicle you have but, generally you need a good set of SAE and Metric tools, sockets and wrenches. You will need at least one specialty tool to remove and replace the pulley without damage. This would be a power steering pulley puller. Most auto parts stores will either sell one or rent one for you. Also, a good shop manual for that vehicle would not hurt.