I cant pull the string to start the mower

SOURCE: mower will not start. starter is stuck.

Is this solved?

SOURCE: Mower hit a big rock and stoped running

If you hit something hard enough to partially shear the key on the blade adapter, you did shear the key on the flywheel, and it will need to be replaced for the engine to run properly.

SOURCE: Pull rope seems to be locked up...won't pull

make sure you can turn the blade by hand, make sure grass isn't stopping the blade after that make sure the break cable isn't bad, sometime's the cable don't disengage the break from the flywheel. Hope this works.

SOURCE: I have a briggs and stratton quicksilver, just got

Not to worry. When you tipped the mower on its side, oil ran into the exhaust. Allow the engine to run few minutes and it will stop smoking. The B&S engine will put oil in the muffler if tipped to the left, and oil into the carburetor if tipped on the right. The only safe way to tip the engine is where the spark plug is pointed upward.
Don't forget to check your oil level and adjust as necessary.
Good luck!

Testimonial: "i will try what you suggested, i did tip it on the side you described, but thought engine had gone... it still runs so you must be right thankyou"

SOURCE: mower is making a clunking

I think that noise is because your blades are loose. They should be tightened right away because they could come off when you are using it with the possibility of injury to somebody. I have serviced some mowers with that problem. They make more noise when starting because they are turning slow and moving around more than when turning at high speed. Best regards and good luck.