Viruses can change a lot, depending on what type...
Check your HOSTS file: C:\Windows\System32\Drivers\Etc
Once you have found your HOSTS file, right-click on the HOSTS file, and then select Open. You will be asked to choose a program to use. Select Notepad, but make sure you that you do NOT turn on any option to always use the same program.
Anything else that appears in your HOSTS file without an # at the beginning, apart from the "127.0.0.1 localhost" line, should be viewed with suspicion when we are trying to diagnose the cause of "Page cannot be displayed" errors. You can temporary comment them with # at the front of the line to check. Reply back if you think there is something fishy added to your hosts.
Sometimes Internet Explorer is unable to access the Internet if software known as Layered Service Provider (LSP) has been removed incorrectly from a computer or previously infected.
Start, then Run and type CMD in the dialogue box that appears, and then click OK. Type netsh winsock reset into the DOS window that appears.