Pull string wont budge.

So pulled out the ol lawnmower Honda HRN216. Morot was hydrolocked so I remedied it by taking out the spark plus and pulling it a few times, worked like a charm I was mowing in just a few minutes no problems at all. Then it shut off about half the yard done. So I tried the method again took the plug out and pulled and to my surprise the string wouldn't budge.. any help would be appreciated.