FS 2004 Radio problem

Can anyone help me on the next situation please:
Suddenly the com/nav radios of the default aircraft in FS 2004 (as well as any downloaded a/c using the default radios) are frozen. Impossible to change frequencies.
There is no apparent reason.
I have tried to overcome the problem by reloading the default aircraft (including the applicable gauges) but no joy.
Any suggestions?
Thanks,
Ron
Suddenly the com/nav radios of the default aircraft in FS 2004 (as well as any downloaded a/c using the default radios) are frozen. Impossible to change frequencies.
There is no apparent reason.
I have tried to overcome the problem by reloading the default aircraft (including the applicable gauges) but no joy.
Any suggestions?
Thanks,
Ron