pragma solidity ^0.4.7;
contract SimpleStorage {

  uint public storedData;
  string public name = "ahmed";
  event Print(uint);

  function SimpleStorage(uint initialValue) {
    storedData = initialValue;
  }

  function set(uint x) returns (uint){
    storedData = x;
    Print(storedData);
    return storedData;
  }

  function get() constant returns (uint retVal) {
    return storedData;
  }
}

Error: Invalid JSON RPC response: ""

web3 = new Web3(new Web3.providers.HttpProvider("https://ropsten.infura.io/ahmed_charef"));

contractAddress = "0x752fB8626c5bEf519EfC661F6694fbE497405FfE"
ABI  = [{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"storedData","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"x","type":"uint256"}],"name":"set","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"get","outputs":[{"name":"retVal","type":"uint256"}],"payable":false,"type":"function"},{"inputs":[{"name":"initialValue","type":"uint256"}],"payable":false,"type":"constructor"},{"anonymous":false,"inputs":[{"indexed":false,"name":"","type":"uint256"}],"name":"Print","type":"event"}]

myContract = web3.eth.contract(ABI).at(contractAddress);

myContract.name(function(err, res){
    console.log(res);
  })

function voteForCand() {

  myContract.set("20");
}