intermitant fault

[slicer]

pc working fine until 2 days ago.now i can still get on to internet but nearly every second page comes back saying unable to display using IE8 and connection to server was reset when using firefox. when using namsco speedtest download speed is fine but unable to carryout upload. have run a scan and nothing detected have restored back to an earlier date and have reset pc to factory settings but still the same. other pc working off of same adsl connection works fine so can rule that out. pc is a dell inspiron 530 with vista. any help would be much appreciated. thanks.   

[truenorth]

sliser,Welcome to the CH forums. Most often things that "change" (as in your access to web pages) are as a result of some change done to the computer (hardware/software). What if any changes were done coincident with the appearance of this situation/ truenorth