|If I remember correctly, Firefox pops up a box that says it is virus checking. Internet Explorer says nothing and just sits there at 99%. It confused me too until I found that if I waited long enough the screen closed and it was fine.|
The wait probably depends on whose virus checker you are using.
If the above is the case there is little anyone can do except either turning off their virus checker (obviously not recommended) or trying a different AV.
Always pop back and let us know the outcome - thanks