Have you aliased the command to some other command.
Try this
alias gnome-terminal
If it has someother command along with it ,then that command is not getting exectuted.
Or if you are in GUI
right click on Gnome terminal,check the Command and correct it.
Ex:
If the command has been aliased like this
gnome-terminal | someothercommand
then someothercommand may be creaeting a problem.
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