|You probably need to install the software that came with the keyboard again.|
Go to Control Panel> keyboard. Verify the correct type/model is listed there. Windows can usually configure Microsoft keyboards. Others probably need the software installed.
If you didn't change any files in your computer you could try to remove the keyboard from within Device Manager and then reboot. If the correct drivers are still present, then Windows should re-install the keyboard with the extras features.
You could also check recent updates from MS to see if something related to the keyboard was recently installed. Look at add/remove programs in Control Panel. Be sure that "show updates" is checked.