Internet doesn't work on Win 7 Home Premium

Hi I have a strange problem.

The system was working fine for 3-4 months and suddenly it started giving me the below problems
Background:

• OS > Windows 7 Home Premium
• System is connected to internet and its works great on IE8.
• Ram - 4GB DDR

Problem:

• Internet works only for IE8
• All the messengers (Gtalk, Yahoo, MSN, ICQ) says that the system is not connected to Internet.
• All the windows inbuilt functions (eg Win Help) says that the system is not connected to Internet.
• All the other browsers (Firefox, Chrome, Safari & Opera) says that the system is not connected to Internet.
• Antivirus softwares doesn't work. And are not able to do live update.

All the problem list has same reason " System is not connected to Internet "

Somebody please help me!!!

Hi zzz2496

I checked the host file and have also scanned the harddrive connected on clean system and nothing was found.

My host file is as below;

# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host
127.0.0.1 localhost
::1 localhost

I tried removing last line but windows is not allowing my to save the changes on the file.

Done all is well.... everything looks ok... checked between two computers and compared the settings and its the same....
restored my system to old "restore point" doesn't work

guess need to re-install the system.