To find out:
- what is displayed in the status bar when you move your mouse pointer onto the tool icon?
- as it is not one of the standard icons in ImageJ or Fiji: which toolset did you activate via the >> menu?
If these don’t help, please check:
- do you auto-run any macros/toolsets at startup? (Plugins › Macros › Startup Macros…)
- which update site do you have activated?