A malware probably modified your Local Area Network (LAN) Settings to redirect your connection.
Check your TCP/IP, Proxy Server and DNS Settings:
1. Click on Start > Control Panel > Network and Internet > Internet Options > Connections > LAN Settings. Make sure that only the "Automatically detect settings" box is marked. The rest (including the Proxy Server) should be left unmarked. Click OK to close.
If you are are also using another browser like Firefox, click on Tools or the orange Firefox tab > Options > Advanced > Network > Connection Settings. Select "No Proxy".
2. For XP, click on Start > Control Panel > Network and Internet Connections > Network Connections. Right click on Local Area Connection. Under General tab, select TCP/IP. Click on Properties > General tab, select "Obtain an IP address automatically" and "Obtain DNS server address automatically". Click OK to close.
For Vista or 7, on the Control Panel, click on Network and Internet > Network and sharing center > Local Area Connection > Properties. Scroll down and look for TCP/IPv4. Click on Properties > General tab, select "Obtain an IP address automatically" and "Obtain DNS server address automatically". Do this for IPv6 also. Click OK to close.
If your browser still can't connect to any website, check your HOSTS file. On a working computer it should look like this:
http://support.microsoft.com/kb/972034
If it's not like that, fix it or manually edit it.