i have a Logitech keyboard (forgot the model) and it has an F Mode key, when its on the F buttons second fuctions are active. e.g. F1 - F4 open word, excel, etc... but as i dont have them installed they do nothing. if you keyboard doesnt have an F mode button or similar try the setpoint drivers (or what ever they are called) should be able to disable it so that F keys work correctly.
simple test would be to boot the computer up and press F8 on start up and if the start windows in safe mode prompt comes up then you will atleast know the keys are working and its just a software/setting problem. hope this helps