check under device manager for the exclamation mark,post it here,may be able to solve it if you cna provide this.alternately,install this drivers:ACPI power manager,hotkey driver should work properly after that.when was the last time you updated your bios?
When you say "function keys" i am assuming they are F1 to F12. You don't need a driver for those to work, they are part of your keyboard. You may need to replace your keyboard or have it repaired by a qualified technician.
But if you are referring to the special shortcut keys on your laptop such as volume control, one touch email or web button sometimes called "hotkeys" then you need a driver. If you can give me the model of your laptop, I may be able to point you to the right location where you can download the driver if you don't have one.