My mower pull string want pull out only about 3"4" inch and therefore I can't start my mower due to the fact

Is the pull handle all the way in or all out except 3/4"? If it is all the way out the spring is probably broke, or at the least you may soak it in penetrant to get it to retract.

If it is in all the way and will not pull check under the mower for build up of grass and check engine oil.. . If it is locked up in the engine you have probably suffered a catastrophic failure.

Don