Generally they don't just 'sieze'... there may be something stuck in it, like a rock or something. May be worthwhile to pull it out, and look at it closely to see if you can diagnose the problem... maybe even open it up and see inside of it.
Not sure how much time you want to invest in it though cause they are fairly cheap to replace (depends on how you value your time), but worst-case scenario, you go to the store, use it as a core for a new one and put it in. regardless, it'll have to come out anyway.
Not sure how much time you want to invest in it though cause they are fairly cheap to replace (depends on how you value your time), but worst-case scenario, you go to the store, use it as a core for a new one and put it in. regardless, it'll have to come out anyway.