How do I get my volume GUI back?

I have an emachines T3256 and I used to have a volume GUI that would pop up when I adjusted the volume using the keyboard volume buttons but one day it just went away. I am running Windows XP SP3.The buttons still work but no GUI pops up on the screen. Control panel says that the keyboard is working properly and I’ve looked at other various settings but nothing has worked. Anyone got any ideas?