First you check wheter any proxy settings are present in Internet Explorer.If present remove it and try.
If not helps
1. HKCU\SOFTWARE\Microsoft\Windows\Currentversion\Internet settings Click on the internet setting key check for the keys called "ProxyEnable" if it is set to 1 then change it to 0 also check if there is a registry value called "GlobalUserOffline" if it is present delete the GlobalUserOffline key
2.Check HKU\.Default\SOFTWARE\Microsoft\Windows\Currentversion\Internet settings Click on the internet setting key check for the keys called "ProxyEnable" if it is set to 1 then change it to 0 also check if there is a registry value called "GlobalUserOffline" if it is present delete the GlobalUserOffline key
3.Reboot the machine.