Gummed up bearings I suspect - you do not say what problem Derek had 3 years ago - the humming suggests the motor is trying to turn - the lack of movement suggests something is preventing it - your question is in the circular saw category - Ah! it's not a food mixer it's a cement mixer - seized gearbox then.
Good luck...
http://www.magic-parts.co.uk/acatalog/Minimix-150.php
Peccavi
May 2013
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