Many times slow opening files point to a virus. To rule that out, go here and run a free scan (select 'Auto Clean'. Note: it may take a little while to load):

http://housecall.trendmicro.com/housecall/start_corp.asp

Also download the new MS anti-spyware beta and let it examine yor system:

http://www.microsoft.com/downloads/details.aspx?FamilyId=321CD7A2-6A57-4C57-A8BD-DBF62EDA9671&displaylang=en