The Microsoft keyboards now have an F-Lock button. The default is for the F keys to be off. If you need to use the F keys to install windows or get into BIOS the F-Lock button has to be pushed in the beginning of POST. Microsoft's idea was to allow keys to do more than one operation.
If you really hate this feature, this F Lock Key Information site offers a zip file that will turn this 'enhanced' feature off and explains how it works.