Robin,
Attached is a snip of the default HEC-GeoHMS toolbar from 10.0.0.95
Two things to try:
1) Use the ArcMap -> Customize -> Customize Mode and highlight the GeoHMS toolbar. Then use the Reset button (see attached images).
2) Delete your user AppData profile (C:\Users\YourUserName\AppData\Local\ESRI and ...\AppData\Roaming\ESRI) and your per user Registry configuration. E.g. HKEY_CURRENT_USER\Software\ESRI.
Then allow them to rebuild with defaults on next launch.
See if either will get you back to default toolbar.
Stuart