F8 Key won't trigger safe mode at startup

I am trying to run a virus scan of my Inspiron 5150 laptop while in safe mode (running Windows XP sp2).  I can't seem to get the machine to boot into safe mode.  I've tried hitting the F8 key (rapidly -- during the whole boot cycle) -- but it just seems to be ignored.  I Googled something that said that some systems respond to F5 instead, but that didn't work either.  Is there some magic, or do I, perhaps have a bad keyboard?  Failing getting into safe mode via F8 during boot, is there some hack to tell XP that the next boot should be into safe mode?

 

Thanks for any advice.