Its either network transmission problem,yr monitor or yr graphic card,try below steps:
1.Borrow yr friend monitor and swap with yr monitor and try to view the web site
2.Take out yr graphic card and put back(|Remember power down yr pc 1st :-p)
3.If the blue line only appear on certain web site,then mainly caused by the network transmission problem which I don't think you can do anything;either you send an email to the webmaster of the web page to notify them or you stop view that web site.