Hi Zahid,

Sorry for this issue you are facing.

If you are getting a failed to send request error message, you will want to check the server host Data Loader setting. We will show you how to check this, and a few other settings that could be causing the problem.
 
Resolution1. Check the server host - you'll want to make sure that the server host has been set to https://login.salesforce.com or if you're using sandbox, the URL is https://test.salesforce.com. Please review, Configure Data Loader.

2. Check your instance -  if you're unable to connect via the generic server hosts in 1 try connecting to your instance directly via: https://<InstanceHere>.salesforce.com where <InstanceHere> is the Salesforce instance where the org you're attempting to connect to resides. See How to tell what instance of Salesforce my Organization is using for more details on identifying which instance your org resides on.

Please review, View instance information for your Salesforce organization.

3. Check if your network is using a proxy - Getting the error message, "Failed to send request to https://www.salesforce.com/services/Soap/u/31.0" typically indicates that you're going through a proxy server resulting in your login attempt from the Data Loader not making it from your local machine to Salesforce servers. If your network is utilizing a VPN, you'll need to include or set your proxy information in the Data Loader settings. We recommend contacting your IT department to get the following pieces of information:
- Proxy host
- Proxy port
- Proxy username
- Proxy password settings
 
4. Check network connectivity or local machine issues - Review the affected user record's login history. Please review, Monitor Login History. If the Data Loader's login attempt has been recorded, you'll want to check the login attempt status. You'll be looking for login attempts that failed due to:
- Incorrect password
- Login restrictions
- Missing a required security token. (Please review, Reset Your Security Token.)

If no login attempt has been recorded, check that the correct username and server host setting is being used. Once you've confirmed that all information is correct, and you're still not seeing a login attempt recorded, check your firewall, router, switch, or other network related devices. Please review, Test to determine cause of slowness connecting to Salesforce.

If you continue to experience trouble with the Data Loader, you'll want to try uninstalling and re-installing the latest version found via Setup, Data Management | Data Loader. Alternatively you may consider Install Data Loader on another machine to rule out any local machine issues.

For more information please refer to below link with a similar discussion.

• https://success.salesforce.com/answers?id=90630000000Cy3iAAC

Hope this helps.

Thanks,
Nagendra