"cloud" function doesn't plot

Forgive me please if this has been answered previously, but the r-help 
archive doesn't have a "search" capability. It's a pity, as I'm sure that 
there's a wealth of informative help in there.

I am unable to get the "cloud" function to produce a fundamental 3D 
scatterplot. I have a 3-column numeric matrix:

is.matrix(sanity.MIF); is.numeric(sanity.MIF); dim(sanity.MIF); 
cloud(sanity.MIF)

[1] TRUE
[1] TRUE
[1] 2970    3

A blank grey graphics window is opened, but no vestige of a plot or labels 
of any kind.

Can someone tell me what I am missing please? R 1.7.1 Windows2000 is new to 
me, but plenty of prior S-Plus Unix experience, including the use of the 
"spin" function for rotational 3D scatterplots.

Thank You for your help.