Sorry, wasn't very clear.
Whilst wearing the HRM switch Garmin on, if you get no connection to HRM goto the following menu.
Mode > Settings > General > Set Heart Monitor
Set the HRM to Off, wait a while, then swicth the HRM back to On. After a bit of playing around with this and maybe a few rescans it started working again.
(The on/off is an option in that menu, nothing physically is turned on/off).
Edited: 28/08/2009 at 20:57