If you experience the subject condition, your sound driver may have improperly set the Enable HW Volume Control Value Name to a data value of zero at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\\{4D36E96C-E325-11CE-BFC1-08002BE10318\}\0000.

If your data value is zero, run the following HWVOL.BAT file to set it to one:

@echo off
set key=HKLM\SYSTEM\CurrentControlSet\Control\Class\\{4D36E96C-E325-11CE-BFC1-08002BE10318\}\0000
@echo Retrieve "Enable HW Volume Control"
for /f "Skip=3 Tokens=5" %%i in ('reg QUERY %key% /v "Enable HW Volume Control"') do set type=%%i
If "%type%" EQU "REG_BINARY" goto HWVOL1B
If "%type%" EQU "REG_DWORD" goto HWVOL1D
@echo Not found or bad data type.
goto :FINISH
@echo Set REG_DWORD
reg ADD %key% /v "Enable HW Volume Control" /t REG_DWORD /d 1 /f
goto :FINISH
@echo Set REG_BINARY
reg ADD %key% /v "Enable HW Volume Control" /t REG_BINARY /d 01 /f
NOTE: You must restart your computer for the changes to take effect.

NOTE: REG.EXE is from the Windows 2000 Support Tools.