If you are getting this error on all web sites you visit, it can be a problem with IE caching.

If you are sure you are connected properly to the Internet, but you still get the error “page cannot be displayed” on every web site you visit, try deleting the Index.dat file.

The location of this file is at: C:/Documents and Settings/username/Local Settings/Temporary Internet FIles/Content.IE5
Replace username above with your username in Windows.

Delete the Index.dat file in there and try Internet Explorer again. If this problem was caused by file caching, this should solve the issue.