Make sure enable sounds is on
maybe try 'use pc speakers'

Typically on a desktop system
'use internal beep' would use
the little speaker in the front
of case that is powered off the
motherboard.. with such a setup
a sound card and external speakers
are not needed.. that was sorta
the whole point of /beep ..its
like old school... I'm on a laptop
now and I have mine on 'use internal
beep' but it still uses the regular
speakers.. when I select use pc speakers
it stops working.. I've been using /beep
for over ten years on several systems
and never had trouble with it.. matter
of fact its the only sound I ever use
in mIRC...