[R] dev() error

[Laura Quinn]

I don't know what I have done!! When I try to invoke a display function
via plot(), image() or whatever, my X11 window doesn't appear. I have
tried to type X11() but the following error message is displayed:

> x11()
Error in X11(display, width, height, pointsize, gamma, colortype,
maxcubesize,
:
        unable to start device X11
In addition: Warning message:
unable to open connection to X11 display`'

I have tried dev.cur() and dev.list() but these suggest that only my null
device is active and I am unsure how to activate my X11 device by any
other means!

I'm sure this is a stupid question but could anyone please help?

Thanks in advance..
Laura