|As several browsers are affected it might be a connection problem on that particular computer.|
Bit of a long shot but are you using a large hosts file? If you don't know what I mean then the answer is probably no.
Try this anyway:
Type cmd in the Run box and hit Enter key.
In the black box that arrives type ipconfig /flushdns and hit Enter key.
Note the single space after ipconfig.
Always pop back and let us know the outcome - thanks