First, is this Vista SP2 and fully updated and how do you connect to the internet?
Secondly, regardless of what browser you use, do you have IE9 installed and is it and all it's add-ons up to date?
Thirdly, do you have any other security product installed?
Fourthly: Any other strange happenings, popups etc.?
Forgot to ask... and lastly, when you uninstalled, did you run the MCPR cleanup tool then reboot before installing again? (Linked under Useful Links at the top of the page).