Normally when I adjust sound a graph appears on screen.
The graph is no longer visible on screen when adjustments are made.
Machine is Vista and sound system is Realtek, the original system that came with the laptop.
Sounds like an app that you had installed, likely by Realtek. If you have the original CDs that came with the laptop, you'll probably find the app there. Otherwise, check on Realteks website, support. Along with the drivers, they most likely have these accessory apps there as well.
If you're adjusting your volume with a keyboard button, then very likely the graph comes from the keyboard driver softwares.
I have Realtek; if I adjust the sound using their icon I get a window with various sliders. If I use the keyboard buttons I get a bargraph [courtesy Logitech].