Virus Unkown

I am using wireless tiscali broadband on a windows xp pc. And when browsing internet explorer about 70% of the pages i view dont display and shows ‘The page cannot be displayed’ page, and after going back re-selecting the link or pressing refresh 4 or 5 times the page (sometimes) displays. The pages i am viewing are regular pages such as ebay.co.uk, bbc.co.uk etc. And i have scaned my computer with up-to-date norton scanes and found no virus. Although when i go onto task manager and end 1 of the 7 svhost.exe tasks a box is displayed ‘nt authority system’ sytem restart count down, just like a worm. Whats going on?